diff --git a/composer.json b/composer.json
index 0769a6b6..35956e20 100644
--- a/composer.json
+++ b/composer.json
@@ -18,7 +18,8 @@
         "erusev/parsedown": "1.6.*",
         "twbs/bootstrap": "^3.3",
         "symfony/http-foundation": "^3.3",
-        "psr/container": "^1.0"
+        "psr/container": "^1.0",
+        "psr/log": "^1.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^6.3"
diff --git a/includes/engelsystem_provider.php b/includes/engelsystem_provider.php
index c7734a7c..a9305df5 100644
--- a/includes/engelsystem_provider.php
+++ b/includes/engelsystem_provider.php
@@ -5,9 +5,12 @@ use Engelsystem\Config\Config;
 use Engelsystem\Database\Db;
 use Engelsystem\Exceptions\Handler as ExceptionHandler;
 use Engelsystem\Http\Request;
+use Engelsystem\Logger\EngelsystemLogger;
 use Engelsystem\Renderer\HtmlEngine;
 use Engelsystem\Renderer\Renderer;
+use Psr\Log\LoggerInterface;
 use Symfony\Component\HttpFoundation\Session\Session;
+use Symfony\Component\HttpFoundation\Session\Storage\MockArraySessionStorage;
 
 /**
  * This file includes all needed functions, connects to the db etc.
@@ -89,6 +92,14 @@ Db::connect(
 Db::getPdo()->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
 Db::getPdo()->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
 
+/**
+ * Init logger
+ */
+$logger = new EngelsystemLogger();
+$app->instance('logger', $logger);
+$app->instance(LoggerInterface::class, $logger);
+$app->instance(EngelsystemLogger::class, $logger);
+
 
 /**
  * Include legacy code
@@ -180,6 +191,9 @@ foreach ($includeFiles as $file) {
  * Init application
  */
 $session = new Session();
+if (PHP_SAPI == 'cli') {
+    $session = new Session(new MockArraySessionStorage());
+}
 $app->instance('session', $session);
 $session->start();
 $request->setSession($session);
diff --git a/src/Logger/EngelsystemLogger.php b/src/Logger/EngelsystemLogger.php
new file mode 100644
index 00000000..db46215c
--- /dev/null
+++ b/src/Logger/EngelsystemLogger.php
@@ -0,0 +1,74 @@
+<?php
+
+namespace Engelsystem\Logger;
+
+use Psr\Log\AbstractLogger;
+use Psr\Log\InvalidArgumentException;
+use Psr\Log\LogLevel;
+
+class EngelsystemLogger extends AbstractLogger
+{
+    protected $allowedLevels = [
+        LogLevel::ALERT,
+        LogLevel::CRITICAL,
+        LogLevel::DEBUG,
+        LogLevel::EMERGENCY,
+        LogLevel::ERROR,
+        LogLevel::INFO,
+        LogLevel::NOTICE,
+        LogLevel::WARNING,
+    ];
+
+    /**
+     * Logs with an arbitrary level.
+     *
+     * @TODO: Implement $context['exception']
+     *
+     * @param mixed  $level
+     * @param string $message
+     * @param array  $context
+     *
+     * @throws InvalidArgumentException
+     */
+    public function log($level, $message, array $context = [])
+    {
+        if (!$this->checkLevel($level)) {
+            throw new InvalidArgumentException();
+        }
+
+        $message = $this->interpolate($message, $context);
+
+        LogEntry_create('Logger: ' . $level, $message);
+    }
+
+    /**
+     * Interpolates context values into the message placeholders.
+     *
+     * @param string $message
+     * @param array  $context
+     * @return string
+     */
+    protected function interpolate($message, array $context = [])
+    {
+        foreach ($context as $key => $val) {
+            // check that the value can be casted to string
+            if (is_array($val) || (is_object($val) && !method_exists($val, '__toString'))) {
+                continue;
+            }
+
+            // replace the values of the message
+            $message = str_replace('{' . $key . '}', $val, $message);
+        }
+
+        return $message;
+    }
+
+    /**
+     * @param string $level
+     * @return bool
+     */
+    protected function checkLevel($level)
+    {
+        return in_array($level, $this->allowedLevels);
+    }
+}
diff --git a/test/Logger/EngelsystemLoggerTest.php b/test/Logger/EngelsystemLoggerTest.php
new file mode 100644
index 00000000..da10800d
--- /dev/null
+++ b/test/Logger/EngelsystemLoggerTest.php
@@ -0,0 +1,126 @@
+<?php
+
+namespace Engelsystem\Test\Logger;
+
+use Engelsystem\Logger\EngelsystemLogger;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\InvalidArgumentException;
+use Psr\Log\LoggerInterface;
+use Psr\Log\LogLevel;
+
+class EngelsystemLoggerTest extends TestCase
+{
+    /**
+     * @return LoggerInterface
+     */
+    public function getLogger()
+    {
+        return new EngelsystemLogger();
+    }
+
+    public function testImplements()
+    {
+        $this->assertInstanceOf('Psr\Log\LoggerInterface', $this->getLogger());
+    }
+
+    /**
+     * @dataProvider provideLogLevels
+     * @param string $level
+     */
+    public function testAllLevels($level)
+    {
+        $logger = $this->getLogger();
+
+        LogEntries_clear_all();
+
+        $logger->log($level, 'First log message');
+        $logger->{$level}('Second log message');
+
+        $entries = LogEntries();
+        $this->assertCount(2, $entries);
+    }
+
+    /**
+     * @return string[]
+     */
+    public function provideLogLevels()
+    {
+        return [
+            [LogLevel::ALERT],
+            [LogLevel::CRITICAL],
+            [LogLevel::DEBUG],
+            [LogLevel::EMERGENCY],
+            [LogLevel::ERROR],
+            [LogLevel::INFO],
+            [LogLevel::NOTICE],
+            [LogLevel::WARNING],
+        ];
+    }
+
+    public function testContextReplacement()
+    {
+        $logger = $this->getLogger();
+        LogEntries_clear_all();
+
+        $logger->log(LogLevel::INFO, 'My username is {username}', ['username' => 'Foo']);
+
+        $entry = $this->getLastEntry();
+        $this->assertEquals('My username is Foo', $entry['message']);
+        $this->assertContains(LogLevel::INFO, $entry['nick'], '', true);
+
+        foreach (
+            [
+                ['Data and {context}', []],
+                ['Data and ', ['context' => null]],
+                ['Data and {context}', ['context' => new \stdClass()]],
+            ] as $data
+        ) {
+            list($result, $context) = $data;
+
+            $logger->log(LogLevel::INFO, 'Data and {context}', $context);
+
+            $entry = $this->getLastEntry();
+            $this->assertEquals($result, $entry['message']);
+        }
+    }
+
+    public function testContextToString()
+    {
+        $logger = $this->getLogger();
+        LogEntries_clear_all();
+
+        $mock = $this->getMockBuilder('someDataProvider')
+            ->setMethods(['__toString'])
+            ->getMock();
+
+        $mock->expects($this->atLeastOnce())
+            ->method('__toString')
+            ->will($this->returnValue('FooBar'));
+
+        $logger->log(LogLevel::INFO, 'Some data and {context}', ['context' => $mock]);
+
+        $entry = $this->getLastEntry();
+        $this->assertEquals('Some data and FooBar', $entry['message']);
+    }
+
+    /**
+     * @expectedException InvalidArgumentException
+     */
+    public function testThrowExceptionOnInvalidLevel()
+    {
+        $logger = $this->getLogger();
+
+        $logger->log('This log level should never be defined', 'Some message');
+    }
+
+    /**
+     * @return array
+     */
+    public function getLastEntry()
+    {
+        $entries = LogEntries();
+        $entry = array_pop($entries);
+
+        return $entry;
+    }
+}