diff --git a/src/Prometheus/CollectorRegistry.php b/src/Prometheus/CollectorRegistry.php
index 9ff18e3..23e0965 100644
--- a/src/Prometheus/CollectorRegistry.php
+++ b/src/Prometheus/CollectorRegistry.php
@@ -9,7 +9,7 @@
 use Prometheus\Storage\Adapter;
 use Prometheus\Storage\Redis;
 
-class CollectorRegistry
+class CollectorRegistry implements RegistryInterface
 {
     /**
      * @var CollectorRegistry
diff --git a/src/Prometheus/RegistryInterface.php b/src/Prometheus/RegistryInterface.php
new file mode 100644
index 0000000..7bae64d
--- /dev/null
+++ b/src/Prometheus/RegistryInterface.php
@@ -0,0 +1,106 @@
+<?php
+
+namespace Prometheus;
+
+use Prometheus\Exception\MetricNotFoundException;
+use Prometheus\Exception\MetricsRegistrationException;
+
+interface RegistryInterface
+{
+    /**
+     * @return MetricFamilySamples[]
+     */
+    public function getMetricFamilySamples();
+
+    /**
+     * @param string $namespace e.g. cms
+     * @param string $name e.g. duration_seconds
+     * @param string $help e.g. The duration something took in seconds.
+     * @param array  $labels e.g. ['controller', 'action']
+     *
+     * @return Gauge
+     * @throws MetricsRegistrationException
+     */
+    public function registerGauge($namespace, $name, $help, $labels = []);
+
+    /**
+     * @param string $namespace
+     * @param string $name
+     *
+     * @return Gauge
+     * @throws MetricNotFoundException
+     */
+    public function getGauge($namespace, $name);
+
+    /**
+     * @param string $namespace e.g. cms
+     * @param string $name e.g. duration_seconds
+     * @param string $help e.g. The duration something took in seconds.
+     * @param array  $labels e.g. ['controller', 'action']
+     *
+     * @return Gauge
+     */
+    public function getOrRegisterGauge($namespace, $name, $help, $labels = []);
+
+    /**
+     * @param string $namespace e.g. cms
+     * @param string $name e.g. requests
+     * @param string $help e.g. The number of requests made.
+     * @param array  $labels e.g. ['controller', 'action']
+     *
+     * @return Counter
+     * @throws MetricsRegistrationException
+     */
+    public function registerCounter($namespace, $name, $help, $labels = []);
+
+    /**
+     * @param string $namespace
+     * @param string $name
+     *
+     * @return Counter
+     * @throws MetricNotFoundException
+     */
+    public function getCounter($namespace, $name);
+
+    /**
+     * @param string $namespace e.g. cms
+     * @param string $name e.g. requests
+     * @param string $help e.g. The number of requests made.
+     * @param array  $labels e.g. ['controller', 'action']
+     *
+     * @return Counter
+     */
+    public function getOrRegisterCounter($namespace, $name, $help, $labels = []);
+
+    /**
+     * @param string $namespace e.g. cms
+     * @param string $name e.g. duration_seconds
+     * @param string $help e.g. A histogram of the duration in seconds.
+     * @param array  $labels e.g. ['controller', 'action']
+     * @param array  $buckets e.g. [100, 200, 300]
+     *
+     * @return Histogram
+     * @throws MetricsRegistrationException
+     */
+    public function registerHistogram($namespace, $name, $help, $labels = [], $buckets = null);
+
+    /**
+     * @param string $namespace
+     * @param string $name
+     *
+     * @return Histogram
+     * @throws MetricNotFoundException
+     */
+    public function getHistogram($namespace, $name);
+
+    /**
+     * @param string $namespace e.g. cms
+     * @param string $name e.g. duration_seconds
+     * @param string $help e.g. A histogram of the duration in seconds.
+     * @param array  $labels e.g. ['controller', 'action']
+     * @param array  $buckets e.g. [100, 200, 300]
+     *
+     * @return Histogram
+     */
+    public function getOrRegisterHistogram($namespace, $name, $help, $labels = [], $buckets = null);
+}
diff --git a/src/Prometheus/RenderTextFormat.php b/src/Prometheus/RenderTextFormat.php
index 95fe2b5..bf7e6a0 100644
--- a/src/Prometheus/RenderTextFormat.php
+++ b/src/Prometheus/RenderTextFormat.php
@@ -3,7 +3,7 @@
 namespace Prometheus;
 
 
-class RenderTextFormat
+class RenderTextFormat implements RendererInterface
 {
     const MIME_TYPE = 'text/plain; version=0.0.4';
 
diff --git a/src/Prometheus/RendererInterface.php b/src/Prometheus/RendererInterface.php
new file mode 100644
index 0000000..ad25258
--- /dev/null
+++ b/src/Prometheus/RendererInterface.php
@@ -0,0 +1,14 @@
+<?php
+declare(strict_types=1);
+
+namespace Prometheus;
+
+interface RendererInterface
+{
+    /**
+     * @param MetricFamilySamples[] $metrics
+     *
+     * @return string
+     */
+    public function render(array $metrics);
+}