diff --git a/composer.json b/composer.json
index 69262e6..35db76d 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,8 @@
     },
     "require-dev": {
         "phpspec/phpspec": "^2.4",
-        "henrikbjorn/phpspec-code-coverage" : "^1.0"
+        "henrikbjorn/phpspec-code-coverage" : "^1.0",
+        "guzzlehttp/psr7": "^1.4"
     },
     "suggest": {
         "php-http/logger-plugin": "PSR-3 Logger plugin",
diff --git a/spec/Plugin/ContentTypePluginSpec.php b/spec/Plugin/ContentTypePluginSpec.php
new file mode 100644
index 0000000..3df7d87
--- /dev/null
+++ b/spec/Plugin/ContentTypePluginSpec.php
@@ -0,0 +1,109 @@
+<?php
+
+namespace spec\Http\Client\Common\Plugin;
+
+use PhpSpec\Exception\Example\SkippingException;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\StreamInterface;
+use PhpSpec\ObjectBehavior;
+use Prophecy\Argument;
+
+class ContentTypePluginSpec extends ObjectBehavior
+{
+    function it_is_initializable()
+    {
+        $this->shouldHaveType('Http\Client\Common\Plugin\ContentTypePlugin');
+    }
+
+    function it_is_a_plugin()
+    {
+        $this->shouldImplement('Http\Client\Common\Plugin');
+    }
+
+    function it_adds_json_content_type_header(RequestInterface $request)
+    {
+        $request->hasHeader('Content-Type')->shouldBeCalled()->willReturn(false);
+        $request->getBody()->shouldBeCalled()->willReturn(\GuzzleHttp\Psr7\stream_for(json_encode(['foo' => 'bar'])));
+        $request->withHeader('Content-Type', 'application/json')->shouldBeCalled()->willReturn($request);
+
+        $this->handleRequest($request, function () {}, function () {});
+    }
+
+    function it_adds_xml_content_type_header(RequestInterface $request)
+    {
+        $request->hasHeader('Content-Type')->shouldBeCalled()->willReturn(false);
+        $request->getBody()->shouldBeCalled()->willReturn(\GuzzleHttp\Psr7\stream_for('<foo>bar</foo>'));
+        $request->withHeader('Content-Type', 'application/xml')->shouldBeCalled()->willReturn($request);
+
+        $this->handleRequest($request, function () {}, function () {});
+    }
+
+    function it_does_not_set_content_type_header(RequestInterface $request)
+    {
+        $request->hasHeader('Content-Type')->shouldBeCalled()->willReturn(false);
+        $request->getBody()->shouldBeCalled()->willReturn(\GuzzleHttp\Psr7\stream_for('foo'));
+        $request->withHeader('Content-Type', null)->shouldNotBeCalled();
+
+        $this->handleRequest($request, function () {}, function () {});
+    }
+
+    function it_does_not_set_content_type_header_if_already_one(RequestInterface $request)
+    {
+        $request->hasHeader('Content-Type')->shouldBeCalled()->willReturn(true);
+        $request->getBody()->shouldNotBeCalled()->willReturn(\GuzzleHttp\Psr7\stream_for('foo'));
+        $request->withHeader('Content-Type', null)->shouldNotBeCalled();
+
+        $this->handleRequest($request, function () {}, function () {});
+    }
+
+    function it_does_not_set_content_type_header_if_size_0_or_unknown(RequestInterface $request)
+    {
+        $request->hasHeader('Content-Type')->shouldBeCalled()->willReturn(false);
+        $request->getBody()->shouldBeCalled()->willReturn(\GuzzleHttp\Psr7\stream_for());
+        $request->withHeader('Content-Type', null)->shouldNotBeCalled();
+
+        $this->handleRequest($request, function () {}, function () {});
+    }
+
+    function it_adds_xml_content_type_header_if_size_limit_is_not_reached_using_default_value(RequestInterface $request)
+    {
+        $this->beConstructedWith([
+            'skip_detection' => true
+        ]);
+
+        $request->hasHeader('Content-Type')->shouldBeCalled()->willReturn(false);
+        $request->getBody()->shouldBeCalled()->willReturn(\GuzzleHttp\Psr7\stream_for('<foo>bar</foo>'));
+        $request->withHeader('Content-Type', 'application/xml')->shouldBeCalled()->willReturn($request);
+
+        $this->handleRequest($request, function () {}, function () {});
+    }
+
+    function it_adds_xml_content_type_header_if_size_limit_is_not_reached(RequestInterface $request)
+    {
+        $this->beConstructedWith([
+            'skip_detection' => true,
+            'size_limit' => 32000000
+        ]);
+
+        $request->hasHeader('Content-Type')->shouldBeCalled()->willReturn(false);
+        $request->getBody()->shouldBeCalled()->willReturn(\GuzzleHttp\Psr7\stream_for('<foo>bar</foo>'));
+        $request->withHeader('Content-Type', 'application/xml')->shouldBeCalled()->willReturn($request);
+
+        $this->handleRequest($request, function () {}, function () {});
+    }
+
+    function it_does_not_set_content_type_header_if_size_limit_is_reached(RequestInterface $request)
+    {
+        $this->beConstructedWith([
+            'skip_detection' => true,
+            'size_limit' => 8
+        ]);
+
+        $request->hasHeader('Content-Type')->shouldBeCalled()->willReturn(false);
+        $request->getBody()->shouldBeCalled()->willReturn(\GuzzleHttp\Psr7\stream_for('<foo>bar</foo>'));
+        $request->withHeader('Content-Type', null)->shouldNotBeCalled();
+
+        $this->handleRequest($request, function () {}, function () {});
+    }
+
+}
diff --git a/src/Plugin/ContentTypePlugin.php b/src/Plugin/ContentTypePlugin.php
new file mode 100644
index 0000000..038b3e4
--- /dev/null
+++ b/src/Plugin/ContentTypePlugin.php
@@ -0,0 +1,123 @@
+<?php
+
+namespace Http\Client\Common\Plugin;
+
+use Http\Client\Common\Plugin;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\StreamInterface;
+use Symfony\Component\OptionsResolver\OptionsResolver;
+
+/**
+ * Allow to set the correct content type header on the request automatically only if it is not set.
+ *
+ * @author Karim Pinchon <karim.pinchon@gmail.com>
+ */
+final class ContentTypePlugin implements Plugin
+{
+    /**
+     * Allow to disable the content type detection when stream is too large (as it can consume a lot of resource).
+     *
+     * @var bool
+     *
+     * true     skip the content type detection
+     * false    detect the content type (default value)
+     */
+    protected $skipDetection;
+
+    /**
+     * Determine the size stream limit for which the detection as to be skipped (default to 16Mb).
+     *
+     * @var int
+     */
+    protected $sizeLimit;
+
+    /**
+     * @param array $config {
+     *
+     *     @var bool $skip_detection True skip detection if stream size is bigger than $size_limit.
+     *     @var int $size_limit size stream limit for which the detection as to be skipped.
+     * }
+     */
+    public function __construct(array $config = [])
+    {
+        $resolver = new OptionsResolver();
+        $resolver->setDefaults([
+            'skip_detection' => false,
+            'size_limit' => 16000000,
+        ]);
+        $resolver->setAllowedTypes('skip_detection', 'bool');
+        $resolver->setAllowedTypes('size_limit', 'int');
+
+        $options = $resolver->resolve($config);
+
+        $this->skipDetection = $options['skip_detection'];
+        $this->sizeLimit = $options['size_limit'];
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function handleRequest(RequestInterface $request, callable $next, callable $first)
+    {
+        if (!$request->hasHeader('Content-Type')) {
+            $stream = $request->getBody();
+            $streamSize = $stream->getSize();
+
+            if (!$stream->isSeekable()) {
+                return $next($request);
+            }
+
+            if (0 === $streamSize) {
+                return $next($request);
+            }
+
+            if ($this->skipDetection && (null === $streamSize || $streamSize >= $this->sizeLimit)) {
+                return $next($request);
+            }
+
+            if ($this->isJson($stream)) {
+                $request = $request->withHeader('Content-Type', 'application/json');
+
+                return $next($request);
+            }
+
+            if ($this->isXml($stream)) {
+                $request = $request->withHeader('Content-Type', 'application/xml');
+
+                return $next($request);
+            }
+        }
+
+        return $next($request);
+    }
+
+    /**
+     * @param $stream StreamInterface
+     *
+     * @return bool
+     */
+    private function isJson($stream)
+    {
+        $stream->rewind();
+
+        json_decode($stream->getContents());
+
+        return json_last_error() == JSON_ERROR_NONE;
+    }
+
+    /**
+     * @param $stream StreamInterface
+     *
+     * @return \SimpleXMLElement|false
+     */
+    private function isXml($stream)
+    {
+        $stream->rewind();
+
+        $previousValue = libxml_use_internal_errors(true);
+        $isXml = simplexml_load_string($stream->getContents());
+        libxml_use_internal_errors($previousValue);
+
+        return $isXml;
+    }
+}