diff --git a/src/Meritoo/LimeSurvey/ApiClient/Result/Collection/Participants.php b/src/Meritoo/LimeSurvey/ApiClient/Result/Collection/Participants.php
new file mode 100644
index 0000000..dfa65c9
--- /dev/null
+++ b/src/Meritoo/LimeSurvey/ApiClient/Result/Collection/Participants.php
@@ -0,0 +1,143 @@
+<?php
+
+/**
+ * (c) Meritoo.pl, http://www.meritoo.pl
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Meritoo\LimeSurvey\ApiClient\Result\Collection;
+
+use Meritoo\Common\Collection\Collection;
+use Meritoo\Common\Exception\Method\DisabledMethodException;
+use Meritoo\LimeSurvey\ApiClient\Result\Item\Participant;
+
+/**
+ * Participants of survey.
+ * All participants grouped per survey.
+ *
+ * It's a collection of participants' collections.
+ * The survey ID is used as an index per each collection of participants, so they are grouped by survey.
+ *
+ * @author    Krzysztof Niziol <krzysztof.niziol@meritoo.pl>
+ * @copyright Meritoo.pl
+ */
+class Participants extends Collection
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function add($element, $index = null)
+    {
+        throw new DisabledMethodException(__METHOD__, 'addParticipants');
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function addMultiple($elements, $useIndexes = false)
+    {
+        throw new DisabledMethodException(__METHOD__, 'addParticipants');
+    }
+
+    /**
+     * Adds participants of given survey
+     *
+     * @param Collection $participants Participants to add. Collection of Participant classes.
+     * @param int        $surveyId     ID of survey
+     * @return $this
+     */
+    public function addParticipants(Collection $participants, $surveyId)
+    {
+        /*
+         * No participants?
+         * Nothing to do
+         */
+        if ($participants->isEmpty()) {
+            return $this;
+        }
+
+        $this
+            ->getBySurvey($surveyId)
+            ->addMultiple($participants);
+
+        return $this;
+    }
+
+    /**
+     * Adds participant of given survey
+     *
+     * @param Participant $participant Participant to add
+     * @param int         $surveyId    ID of survey
+     * @return $this
+     */
+    public function addParticipant(Participant $participant, $surveyId)
+    {
+        $this
+            ->getBySurvey($surveyId)
+            ->add($participant);
+
+        return $this;
+    }
+
+    /**
+     * Returns information if there are participants of given survey
+     *
+     * @param int $surveyId ID of survey
+     * @return bool
+     */
+    public function hasParticipantsOfSurvey($surveyId)
+    {
+        return false === $this
+                ->getBySurvey($surveyId)
+                ->isEmpty();
+    }
+
+    /**
+     * Returns participants of given survey
+     *
+     * If there are no participants of given survey, adds an empty collection who will store participants.
+     * So, this method will return collection always.
+     *
+     * @param int $surveyId ID of survey
+     * @return Collection
+     */
+    public function getBySurvey($surveyId)
+    {
+        /*
+         * There are no participants of given survey?
+         * Let's add an empty collection who will store participants
+         */
+        if (!isset($this[$surveyId])) {
+            $this[$surveyId] = new Collection();
+        }
+
+        return $this[$surveyId];
+    }
+
+    /**
+     * Returns participant of given survey
+     *
+     * @param int    $surveyId         ID of survey
+     * @param string $participantEmail E-mail of searched participant
+     * @return Participant|null
+     */
+    public function getParticipantOfSurvey($surveyId, $participantEmail)
+    {
+        /* @var Collection $participants */
+        $participants = $this->getBySurvey($surveyId);
+
+        if ($participants->isEmpty()) {
+            return null;
+        }
+
+        /* @var Participant $participant */
+        foreach ($participants as $participant) {
+            if ($participant->getEmail() == $participantEmail) {
+                return $participant;
+            }
+        }
+
+        return null;
+    }
+}
diff --git a/src/Meritoo/LimeSurvey/ApiClient/Service/ParticipantService.php b/src/Meritoo/LimeSurvey/ApiClient/Service/ParticipantService.php
new file mode 100644
index 0000000..be672fa
--- /dev/null
+++ b/src/Meritoo/LimeSurvey/ApiClient/Service/ParticipantService.php
@@ -0,0 +1,142 @@
+<?php
+
+/**
+ * (c) Meritoo.pl, http://www.meritoo.pl
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Meritoo\LimeSurvey\ApiClient\Service;
+
+use Meritoo\Common\Collection\Collection;
+use Meritoo\LimeSurvey\ApiClient\Client\Client;
+use Meritoo\LimeSurvey\ApiClient\Result\Collection\Participants;
+use Meritoo\LimeSurvey\ApiClient\Result\Item\Participant;
+use Meritoo\LimeSurvey\ApiClient\Type\MethodType;
+
+/**
+ * Serves participants
+ *
+ * @author    Krzysztof Niziol <krzysztof.niziol@meritoo.pl>
+ * @copyright Meritoo.pl
+ */
+class ParticipantService
+{
+    /**
+     * Client of the LimeSurvey's API
+     *
+     * @var Client
+     */
+    private $client;
+
+    /**
+     * Participants of survey.
+     * All participants grouped per survey.
+     *
+     * @var Participants
+     */
+    private $allParticipants;
+
+    /**
+     * Class constructor
+     *
+     * @param Client       $client          Client of the LimeSurvey's API
+     * @param Participants $allParticipants (optional) Participants of survey. All participants grouped per survey.
+     */
+    public function __construct(Client $client, Participants $allParticipants = null)
+    {
+        if (null === $allParticipants) {
+            $allParticipants = new Participants();
+        }
+
+        $this->client = $client;
+        $this->allParticipants = $allParticipants;
+    }
+
+    /**
+     * Returns participants of given survey
+     *
+     * @param int $surveyId ID of survey
+     * @return Collection
+     */
+    public function getSurveyParticipants($surveyId)
+    {
+        $hasSurvey = $this
+            ->allParticipants
+            ->hasParticipantsOfSurvey($surveyId);
+
+        if (!$hasSurvey) {
+            $arguments = [
+                $surveyId,
+            ];
+
+            $participants = $this
+                ->client
+                ->run(MethodType::LIST_PARTICIPANTS, $arguments)
+                ->getData();
+
+            $this
+                ->allParticipants
+                ->addParticipants($participants, $surveyId);
+        }
+
+        return $this
+            ->allParticipants
+            ->getBySurvey($surveyId);
+    }
+
+    /**
+     * Returns information if given survey has participant with given e-mail
+     *
+     * @param int    $surveyId ID of survey
+     * @param string $email    E-mail address of the participant
+     * @return bool
+     */
+    public function hasParticipant($surveyId, $email)
+    {
+        /*
+         * I have to get all participants of survey to avoid problem when participants exist but are not loaded
+         */
+        $this->getSurveyParticipants($surveyId);
+
+        return null !== $this
+                ->allParticipants
+                ->getParticipantOfSurvey($surveyId, $email);
+    }
+
+    /**
+     * Adds participant with given data to survey with given ID
+     *
+     * @param int    $surveyId  ID of survey
+     * @param string $firstName First name of the participant to add
+     * @param string $lastName  Last ame of the participant to add
+     * @param string $email     E-mail address of the participant to add
+     * @return Participant
+     */
+    public function addParticipant($surveyId, $firstName, $lastName, $email)
+    {
+        $participantsData = [
+            [
+                'firstname' => $firstName,
+                'lastname'  => $lastName,
+                'email'     => $email,
+            ],
+        ];
+
+        $arguments = [
+            $surveyId,
+            $participantsData,
+        ];
+
+        $participantCollection = $this
+            ->client
+            ->run(MethodType::ADD_PARTICIPANTS, $arguments)
+            ->getData();
+
+        $this
+            ->allParticipants
+            ->addParticipants($participantCollection, $surveyId);
+
+        return $participantCollection->getFirst();
+    }
+}
diff --git a/tests/Meritoo/LimeSurvey/Test/ApiClient/Result/Collection/ParticipantsTest.php b/tests/Meritoo/LimeSurvey/Test/ApiClient/Result/Collection/ParticipantsTest.php
new file mode 100644
index 0000000..d93e049
--- /dev/null
+++ b/tests/Meritoo/LimeSurvey/Test/ApiClient/Result/Collection/ParticipantsTest.php
@@ -0,0 +1,143 @@
+<?php
+
+/**
+ * (c) Meritoo.pl, http://www.meritoo.pl
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Meritoo\LimeSurvey\Test\ApiClient\Result\Collection;
+
+use Meritoo\Common\Collection\Collection;
+use Meritoo\Common\Exception\Method\DisabledMethodException;
+use Meritoo\Common\Test\Base\BaseTestCase;
+use Meritoo\Common\Type\OopVisibilityType;
+use Meritoo\LimeSurvey\ApiClient\Result\Collection\Participants;
+use Meritoo\LimeSurvey\ApiClient\Result\Item\Participant;
+
+/**
+ * Test case of the participants of survey
+ *
+ * @author    Krzysztof Niziol <krzysztof.niziol@meritoo.pl>
+ * @copyright Meritoo.pl
+ */
+class ParticipantsTest extends BaseTestCase
+{
+    /**
+     * An empty collection of participants
+     *
+     * @var Participants
+     */
+    private $participantsEmpty;
+
+    /**
+     * Participants of 1 survey
+     *
+     * @var Participants
+     */
+    private $participantsOfOneSurvey;
+
+    /**
+     * Participants of more than 1 survey
+     *
+     * @var Participants
+     */
+    private $participantsOfManySurvey;
+
+    public function testConstructorVisibilityAndArguments()
+    {
+        static::assertConstructorVisibilityAndArguments(Participants::class, OopVisibilityType::IS_PUBLIC, 1, 0);
+    }
+
+    public function testAdd()
+    {
+        $this->expectException(DisabledMethodException::class);
+        (new Participants())->add('');
+    }
+
+    public function testAddMultiple()
+    {
+        $this->expectException(DisabledMethodException::class);
+        (new Participants())->addMultiple([]);
+    }
+
+    public function testAddParticipantsWithoutParticipants()
+    {
+        $surveyId = 1;
+
+        $participants = new Participants();
+        $result = $participants->addParticipants(new Collection(), $surveyId);
+
+        static::assertFalse($participants->hasParticipantsOfSurvey($surveyId));
+        static::assertFalse($participants->hasParticipantsOfSurvey(2));
+
+        static::assertEquals($participants, $result);
+        static::assertCount(0, $participants->getBySurvey($surveyId));
+    }
+
+    public function testAddParticipantsFirstParticipants()
+    {
+        $surveyId = 1;
+
+        $participantsData = new Collection([
+            new Participant(),
+            new Participant(),
+        ]);
+
+        $result = $this
+            ->participantsEmpty
+            ->addParticipants($participantsData, $surveyId);
+
+        static::assertTrue($this->participantsEmpty->hasParticipantsOfSurvey($surveyId));
+        static::assertFalse($this->participantsEmpty->hasParticipantsOfSurvey(2));
+
+        static::assertEquals($this->participantsEmpty, $result);
+        static::assertCount(2, $this->participantsEmpty->getBySurvey($surveyId));
+    }
+
+    public function testAddParticipantsMoreParticipants()
+    {
+        $surveyId = 2;
+
+        $participantsData = new Collection([
+            new Participant(),
+            new Participant(),
+        ]);
+
+        $result = $this
+            ->participantsOfOneSurvey
+            ->addParticipants($participantsData, $surveyId);
+
+        static::assertTrue($this->participantsOfOneSurvey->hasParticipantsOfSurvey($surveyId));
+        static::assertFalse($this->participantsOfOneSurvey->hasParticipantsOfSurvey(3));
+
+        static::assertEquals($this->participantsOfOneSurvey, $result);
+        static::assertCount(2, $this->participantsOfOneSurvey->getBySurvey($surveyId));
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function setUp()
+    {
+        parent::setUp();
+
+        $this->participantsEmpty = new Participants();
+        $this->participantsOfOneSurvey = new Participants();
+        $this->participantsOfManySurvey = new Participants();
+
+        $participants1Survey = new Collection();
+        $participants2Survey = new Collection();
+        $participants3Survey = new Collection();
+
+        $this
+            ->participantsOfOneSurvey
+            ->addParticipants($participants1Survey, 1);
+
+        $this
+            ->participantsOfManySurvey
+            ->addParticipants($participants1Survey, 2)
+            ->addParticipants($participants2Survey, 3)
+            ->addParticipants($participants3Survey, 4);
+    }
+}
diff --git a/tests/Meritoo/LimeSurvey/Test/ApiClient/Service/ParticipantServiceTest.php b/tests/Meritoo/LimeSurvey/Test/ApiClient/Service/ParticipantServiceTest.php
new file mode 100644
index 0000000..6606c94
--- /dev/null
+++ b/tests/Meritoo/LimeSurvey/Test/ApiClient/Service/ParticipantServiceTest.php
@@ -0,0 +1,186 @@
+<?php
+
+/**
+ * (c) Meritoo.pl, http://www.meritoo.pl
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Meritoo\LimeSurvey\Test\ApiClient\Service;
+
+use Meritoo\Common\Collection\Collection;
+use Meritoo\Common\Test\Base\BaseTestCase;
+use Meritoo\Common\Type\OopVisibilityType;
+use Meritoo\LimeSurvey\ApiClient\Client\Client;
+use Meritoo\LimeSurvey\ApiClient\Configuration\ConnectionConfiguration;
+use Meritoo\LimeSurvey\ApiClient\Manager\JsonRpcClientManager;
+use Meritoo\LimeSurvey\ApiClient\Manager\SessionManager;
+use Meritoo\LimeSurvey\ApiClient\Result\Collection\Participants;
+use Meritoo\LimeSurvey\ApiClient\Result\Item\Participant;
+use Meritoo\LimeSurvey\ApiClient\Service\ParticipantService;
+use PHPUnit_Framework_MockObject_MockObject;
+
+/**
+ * Test case of the service that serves participants
+ *
+ * @author    Krzysztof Niziol <krzysztof.niziol@meritoo.pl>
+ * @copyright Meritoo.pl
+ */
+class ParticipantServiceTest extends BaseTestCase
+{
+    /**
+     * Serves participants.
+     * Service without participants.
+     *
+     * @var ParticipantService
+     */
+    private $serviceWithoutParticipants;
+
+    /**
+     * Serves participants.
+     * Service with participants.
+     *
+     * @var ParticipantService
+     */
+    private $serviceWithParticipants;
+
+    public function testConstructorVisibilityAndArguments()
+    {
+        static::assertConstructorVisibilityAndArguments(ParticipantService::class, OopVisibilityType::IS_PUBLIC, 2, 1);
+    }
+
+    public function testGetSurveyParticipantsFromEmptyParticipants()
+    {
+        $rpcClientManager = $this->getJsonRpcClientManager(3);
+        $sessionManager = $this->getSessionManager();
+
+        $this->createServiceWithoutParticipants($rpcClientManager, $sessionManager);
+        $this->createServiceWithParticipants($rpcClientManager, $sessionManager);
+
+        static::assertCount(0, $this->serviceWithoutParticipants->getSurveyParticipants(1));
+        static::assertCount(0, $this->serviceWithoutParticipants->getSurveyParticipants(2));
+
+        static::assertCount(2, $this->serviceWithParticipants->getSurveyParticipants(1));
+        static::assertCount(1, $this->serviceWithParticipants->getSurveyParticipants(2));
+        static::assertCount(0, $this->serviceWithParticipants->getSurveyParticipants(3));
+    }
+
+    public function testHasParticipant()
+    {
+        $rpcClientManager = $this->getJsonRpcClientManager(3);
+        $sessionManager = $this->getSessionManager();
+
+        $this->createServiceWithoutParticipants($rpcClientManager, $sessionManager);
+        $this->createServiceWithParticipants($rpcClientManager, $sessionManager);
+
+        static::assertFalse($this->serviceWithoutParticipants->hasParticipant(1, 'john@scott.com'));
+        static::assertFalse($this->serviceWithoutParticipants->hasParticipant(2, 'john@scott.com'));
+
+        static::assertTrue($this->serviceWithParticipants->hasParticipant(1, 'john@scott.com'));
+        static::assertFalse($this->serviceWithParticipants->hasParticipant(2, 'john@scott.com'));
+        static::assertFalse($this->serviceWithParticipants->hasParticipant(3, 'john@scott.com'));
+    }
+
+    public function testAddParticipant()
+    {
+        $firstName = 'John';
+        $lastName = 'Scott';
+        $email = 'john@scott.com';
+        $runMethodCallCount = 1;
+
+        $runMethodCallResults = [
+            [
+                'firstname' => $firstName,
+                'lastname'  => $lastName,
+                'email'     => $email,
+            ],
+        ];
+
+        $rpcClientManager = $this->getJsonRpcClientManager($runMethodCallCount, $runMethodCallResults);
+        $sessionManager = $this->getSessionManager();
+        $this->createServiceWithoutParticipants($rpcClientManager, $sessionManager);
+
+        $result = $this->serviceWithoutParticipants->addParticipant(1, $firstName, $lastName, $email);
+        static::assertInstanceOf(Participant::class, $result);
+    }
+
+    /**
+     * Returns configuration used while connecting to LimeSurvey's API
+     *
+     * @return ConnectionConfiguration
+     */
+    private function getConnectionConfiguration()
+    {
+        return new ConnectionConfiguration('http://test.com', 'test', 'test');
+    }
+
+    /**
+     * Returns manager of session started while connecting to LimeSurvey's API
+     *
+     * @return PHPUnit_Framework_MockObject_MockObject
+     */
+    private function getSessionManager()
+    {
+        return $this->createMock(SessionManager::class);
+    }
+
+    /**
+     * Returns manager of the JsonRPC client used while connecting to LimeSurvey's API
+     *
+     * @param int   $runMethodCallCount   Count of calls of the runMethod() method (who is mocked)
+     * @param array $runMethodCallResults (optional) Results of calls of the runMethod() method (who is mocked)
+     * @return PHPUnit_Framework_MockObject_MockObject
+     */
+    private function getJsonRpcClientManager($runMethodCallCount, array $runMethodCallResults = [])
+    {
+        $rpcClientManager = $this->createMock(JsonRpcClientManager::class);
+
+        $rpcClientManager
+            ->expects(static::exactly($runMethodCallCount))
+            ->method('runMethod')
+            ->will(static::returnValue($runMethodCallResults));
+
+        return $rpcClientManager;
+    }
+
+    /**
+     * Creates instance of the tested service without participants
+     *
+     * @param PHPUnit_Framework_MockObject_MockObject $rpcClientManager Manager of the JsonRPC client used while connecting to LimeSurvey's API
+     * @param PHPUnit_Framework_MockObject_MockObject $sessionManager   Manager of session started while connecting to LimeSurvey's API
+     */
+    private function createServiceWithoutParticipants(PHPUnit_Framework_MockObject_MockObject $rpcClientManager, PHPUnit_Framework_MockObject_MockObject $sessionManager)
+    {
+        $configuration = $this->getConnectionConfiguration();
+        $client = new Client($configuration, $rpcClientManager, $sessionManager);
+        $this->serviceWithoutParticipants = new ParticipantService($client);
+    }
+
+    /**
+     * Creates instance of the tested service with participants
+     *
+     * @param PHPUnit_Framework_MockObject_MockObject $rpcClientManager Manager of the JsonRPC client used while connecting to LimeSurvey's API
+     * @param PHPUnit_Framework_MockObject_MockObject $sessionManager   Manager of session started while connecting to LimeSurvey's API
+     */
+    private function createServiceWithParticipants(PHPUnit_Framework_MockObject_MockObject $rpcClientManager, PHPUnit_Framework_MockObject_MockObject $sessionManager)
+    {
+        $configuration = $this->getConnectionConfiguration();
+        $client = new Client($configuration, $rpcClientManager, $sessionManager);
+
+        $allParticipants = new Participants([
+            1 => new Collection([
+                (new Participant())->setValues([
+                    'firstname' => 'John',
+                    'lastname'  => 'Scott',
+                    'email'     => 'john@scott.com',
+                ]),
+                new Participant(),
+            ]),
+            2 => new Collection([
+                new Participant(),
+            ]),
+        ]);
+
+        $this->serviceWithParticipants = new ParticipantService($client, $allParticipants);
+    }
+}