diff --git a/README.md b/README.md
index 6dc36de..3c3ae19 100644
--- a/README.md
+++ b/README.md
@@ -10,9 +10,9 @@ If using Redis, we recommend to run a local Redis instance next to your PHP work
 ## How does it work?
 
 Usually PHP worker processes don't share any state.
-You can pick from two adapters.
-One uses Redis the other APC.
-While the former needs a separate binary running, the latter just needs the [APC](https://pecl.php.net/package/APCU) extension to be installed.
+You can pick from three adapters.
+Redis, APC or an in memory adapter.
+While the first needs a separate binary running, the second just needs the [APC](https://pecl.php.net/package/APCU) extension to be installed. If you don't need persistent metrics between requests (e.g. a long running cron job or script) the in memory adapter might be suitable to use.
 
 ## Usage
 
@@ -73,6 +73,17 @@ Change the Redis options (the example shows the defaults):
 );
 ```
 
+Using the InMemory storage:
+```php
+$registry = new CollectorRegistry(new InMemory());
+
+$counter = $registry->registerCounter('test', 'some_counter', 'it increases', ['type']);
+$counter->incBy(3, ['blue']);
+
+$renderer = new RenderTextFormat();
+$result = $renderer->render($registry->getMetricFamilySamples());
+```
+
 Also look at the [examples](examples).
 
 ## Development
diff --git a/examples/flush_adapter.php b/examples/flush_adapter.php
index 5c58091..0c3862d 100644
--- a/examples/flush_adapter.php
+++ b/examples/flush_adapter.php
@@ -3,14 +3,15 @@
 
 $adapter = $_GET['adapter'];
 
-if ($adapter == 'redis') {
+if ($adapter === 'redis') {
     define('REDIS_HOST', isset($_SERVER['REDIS_HOST']) ? $_SERVER['REDIS_HOST'] : '127.0.0.1');
 
     $redisAdapter = new Prometheus\Storage\Redis(array('host' => REDIS_HOST));
     $redisAdapter->flushRedis();
-}
-
-if ($adapter == 'apc') {
+} elseif ($adapter === 'apc') {
     $apcAdapter = new Prometheus\Storage\APC();
     $apcAdapter->flushAPC();
-}
+} elseif ($adapter === 'in-memory') {
+    $inMemoryAdapter = new Prometheus\Storage\InMemory();
+    $inMemoryAdapter->flushMemory();
+}
\ No newline at end of file
diff --git a/examples/metrics.php b/examples/metrics.php
index 79c0f92..fa89247 100644
--- a/examples/metrics.php
+++ b/examples/metrics.php
@@ -8,12 +8,13 @@
 
 $adapter = $_GET['adapter'];
 
-if ($adapter == 'redis') {
+if ($adapter === 'redis') {
     Redis::setDefaultOptions(array('host' => isset($_SERVER['REDIS_HOST']) ? $_SERVER['REDIS_HOST'] : '127.0.0.1'));
     $adapter = new Prometheus\Storage\Redis();
-}
-if ($adapter == 'apc') {
+} elseif ($adapter === 'apc') {
     $adapter = new Prometheus\Storage\APC();
+} elseif ($adapter === 'in-memory') {
+    $adapter = new Prometheus\Storage\InMemory();
 }
 $registry = new CollectorRegistry($adapter);
 $renderer = new RenderTextFormat();
diff --git a/examples/pushgateway.php b/examples/pushgateway.php
index e92baae..984035d 100644
--- a/examples/pushgateway.php
+++ b/examples/pushgateway.php
@@ -1,9 +1,20 @@
 <?php
 require __DIR__ . '/../vendor/autoload.php';
 
+use Prometheus\Storage\Redis;
 use Prometheus\CollectorRegistry;
 
-$adapter = new Prometheus\Storage\APC();
+$adapter = $_GET['adapter'];
+
+if ($adapter === 'redis') {
+    Redis::setDefaultOptions(array('host' => isset($_SERVER['REDIS_HOST']) ? $_SERVER['REDIS_HOST'] : '127.0.0.1'));
+    $adapter = new Prometheus\Storage\Redis();
+} elseif ($adapter === 'apc') {
+    $adapter = new Prometheus\Storage\APC();
+} elseif ($adapter === 'in-memory') {
+    $adapter = new Prometheus\Storage\InMemory();
+}
+
 $registry = new CollectorRegistry($adapter);
 
 $counter = $registry->registerCounter('test', 'some_counter', 'it increases', ['type']);
diff --git a/examples/some_counter.php b/examples/some_counter.php
index 738ff22..823bfac 100644
--- a/examples/some_counter.php
+++ b/examples/some_counter.php
@@ -5,16 +5,15 @@
 use Prometheus\CollectorRegistry;
 use Prometheus\Storage\Redis;
 
-error_log('c='. $_GET['c']);
-
 $adapter = $_GET['adapter'];
 
-if ($adapter == 'redis') {
+if ($adapter === 'redis') {
     Redis::setDefaultOptions(array('host' => isset($_SERVER['REDIS_HOST']) ? $_SERVER['REDIS_HOST'] : '127.0.0.1'));
     $adapter = new Prometheus\Storage\Redis();
-}
-if ($adapter == 'apc') {
+} elseif ($adapter === 'apc') {
     $adapter = new Prometheus\Storage\APC();
+} elseif ($adapter === 'in-memory') {
+    $adapter = new Prometheus\Storage\InMemory();
 }
 $registry = new CollectorRegistry($adapter);
 
diff --git a/examples/some_gauge.php b/examples/some_gauge.php
index 65aecc6..b3e2382 100644
--- a/examples/some_gauge.php
+++ b/examples/some_gauge.php
@@ -10,12 +10,13 @@
 
 $adapter = $_GET['adapter'];
 
-if ($adapter == 'redis') {
+if ($adapter === 'redis') {
     Redis::setDefaultOptions(array('host' => isset($_SERVER['REDIS_HOST']) ? $_SERVER['REDIS_HOST'] : '127.0.0.1'));
     $adapter = new Prometheus\Storage\Redis();
-}
-if ($adapter == 'apc') {
+} elseif ($adapter === 'apc') {
     $adapter = new Prometheus\Storage\APC();
+} elseif ($adapter === 'in-memory') {
+    $adapter = new Prometheus\Storage\InMemory();
 }
 $registry = new CollectorRegistry($adapter);
 
diff --git a/examples/some_histogram.php b/examples/some_histogram.php
index 684f9f1..6b34809 100644
--- a/examples/some_histogram.php
+++ b/examples/some_histogram.php
@@ -9,12 +9,13 @@
 
 $adapter = $_GET['adapter'];
 
-if ($adapter == 'redis') {
+if ($adapter === 'redis') {
     Redis::setDefaultOptions(array('host' => isset($_SERVER['REDIS_HOST']) ? $_SERVER['REDIS_HOST'] : '127.0.0.1'));
     $adapter = new Prometheus\Storage\Redis();
-}
-if ($adapter == 'apc') {
+} elseif ($adapter === 'apc') {
     $adapter = new Prometheus\Storage\APC();
+} elseif ($adapter === 'in-memory') {
+    $adapter = new Prometheus\Storage\InMemory();
 }
 $registry = new CollectorRegistry($adapter);
 
diff --git a/src/Prometheus/Storage/InMemory.php b/src/Prometheus/Storage/InMemory.php
index 758d19c..37c24b1 100644
--- a/src/Prometheus/Storage/InMemory.php
+++ b/src/Prometheus/Storage/InMemory.php
@@ -3,69 +3,262 @@
 namespace Prometheus\Storage;
 
 
-use Prometheus\Collector;
 use Prometheus\MetricFamilySamples;
-use Prometheus\Sample;
 
 class InMemory implements Adapter
 {
-    /**
-     * @var Collector[]
-     */
-    private $metrics = array();
-    /**
-     * @var array
-     */
-    private $samples = array();
+
+    private $counters = [];
+    private $gauges = [];
+    private $histograms = [];
 
     /**
      * @return MetricFamilySamples[]
      */
     public function collect()
     {
-        $responses = array();
-        foreach ($this->metrics as $metric) {
-            $samples = $this->samples[$metric->getKey()];
-            array_multisort($samples);
-            $responses[] = new MetricFamilySamples(
-                array(
-                    'name' => $metric->getName(),
-                    'type' => $metric->getType(),
-                    'help' => $metric->getHelp(),
-                    'samples' => $samples,
-                    'labelNames' => $metric->getLabelNames()
-                )
-            );
+        $metrics = $this->internalCollect($this->counters);
+        $metrics = array_merge($metrics, $this->internalCollect($this->gauges));
+        $metrics = array_merge($metrics, $this->collectHistograms());
+        return $metrics;
+    }
+
+    public function flushMemory()
+    {
+        $this->counters = [];
+        $this->gauges = [];
+        $this->histograms = [];
+    }
+
+    private function collectHistograms()
+    {
+        $histograms = [];
+        foreach ($this->histograms as $histogram) {
+            $metaData = $histogram['meta'];
+            $data = [
+                'name' => $metaData['name'],
+                'help' => $metaData['help'],
+                'type' => $metaData['type'],
+                'labelNames' => $metaData['labelNames'],
+                'buckets' => $metaData['buckets']
+            ];
+
+            // Add the Inf bucket so we can compute it later on
+            $data['buckets'][] = '+Inf';
+
+            $histogramBuckets = [];
+            foreach ($histogram['samples'] as $key => $value) {
+                $parts = explode(':', $key);
+                $labelValues = $parts[2];
+                $bucket = $parts[3];
+                // Key by labelValues
+                $histogramBuckets[$labelValues][$bucket] = $value;
+            }
+
+            // Compute all buckets
+            $labels = array_keys($histogramBuckets);
+            sort($labels);
+            foreach ($labels as $labelValues) {
+                $acc = 0;
+                $decodedLabelValues = json_decode($labelValues);
+                foreach ($data['buckets'] as $bucket) {
+                    $bucket = (string)$bucket;
+                    if (!isset($histogramBuckets[$labelValues][$bucket])) {
+                        $data['samples'][] = [
+                            'name' => $metaData['name'] . '_bucket',
+                            'labelNames' => ['le'],
+                            'labelValues' => array_merge($decodedLabelValues, [$bucket]),
+                            'value' => $acc
+                        ];
+                    } else {
+                        $acc += $histogramBuckets[$labelValues][$bucket];
+                        $data['samples'][] = [
+                            'name' => $metaData['name'] . '_' . 'bucket',
+                            'labelNames' => ['le'],
+                            'labelValues' => array_merge($decodedLabelValues, [$bucket]),
+                            'value' => $acc
+                        ];
+                    }
+                }
+
+                // Add the count
+                $data['samples'][] = [
+                    'name' => $metaData['name'] . '_count',
+                    'labelNames' => [],
+                    'labelValues' => $decodedLabelValues,
+                    'value' => $acc
+                ];
+
+                // Add the sum
+                $data['samples'][] = [
+                    'name' => $metaData['name'] . '_sum',
+                    'labelNames' => [],
+                    'labelValues' => $decodedLabelValues,
+                    'value' => $histogramBuckets[$labelValues]['sum']
+                ];
+
+            }
+            $histograms[] = new MetricFamilySamples($data);
         }
-        array_multisort($responses);
-        return $responses;
+        return $histograms;
     }
 
-    /**
-     * @return Sample[]
-     */
-    public function fetchSamples()
+    private function internalCollect(array $metrics)
     {
-        return array_map(
-            function ($data) { return new Sample($data); },
-            array_values(array_reduce(array_values($this->samples), 'array_merge', array()))
-        );
+        $result = [];
+        foreach ($metrics as $metric) {
+            $metaData = $metric['meta'];
+            $data = [
+                'name' => $metaData['name'],
+                'help' => $metaData['help'],
+                'type' => $metaData['type'],
+                'labelNames' => $metaData['labelNames'],
+            ];
+            foreach ($metric['samples'] as $key => $value) {
+                $parts = explode(':', $key);
+                $labelValues = $parts[2];
+                $data['samples'][] = [
+                    'name' => $metaData['name'],
+                    'labelNames' => [],
+                    'labelValues' => json_decode($labelValues),
+                    'value' => $value
+                ];
+            }
+            $this->sortSamples($data['samples']);
+            $result[] = new MetricFamilySamples($data);
+        }
+        return $result;
     }
 
     public function updateHistogram(array $data)
     {
-        // TODO: Implement incrementByFloat() method.
+        // Initialize the sum
+        $metaKey = $this->metaKey($data);
+        if (array_key_exists($metaKey, $this->histograms) === false) {
+            $this->histograms[$metaKey] = [
+                'meta' => $this->metaData($data),
+                'samples' => []
+            ];
+        }
+        $sumKey = $this->histogramBucketValueKey($data, 'sum');
+        if (array_key_exists($sumKey, $this->histograms[$metaKey]['samples']) === false) {
+            $this->histograms[$metaKey]['samples'][$sumKey] = 0;
+        }
+
+        $this->histograms[$metaKey]['samples'][$sumKey] += $data['value'];
+
+
+        $bucketToIncrease = '+Inf';
+        foreach ($data['buckets'] as $bucket) {
+            if ($data['value'] <= $bucket) {
+                $bucketToIncrease = $bucket;
+                break;
+            }
+        }
+
+        $bucketKey = $this->histogramBucketValueKey($data, $bucketToIncrease);
+        if (array_key_exists($bucketKey, $this->histograms[$metaKey]['samples']) === false) {
+            $this->histograms[$metaKey]['samples'][$bucketKey] = 0;
+        }
+        $this->histograms[$metaKey]['samples'][$bucketKey] += 1;
     }
 
     public function updateGauge(array $data)
     {
-        // TODO: Implement updateGauge() method.
+        $metaKey = $this->metaKey($data);
+        $valueKey = $this->valueKey($data);
+        if (array_key_exists($metaKey, $this->gauges) === false) {
+            $this->gauges[$metaKey] = [
+                'meta' => $this->metaData($data),
+                'samples' => []
+            ];
+        }
+        if (array_key_exists($valueKey, $this->gauges[$metaKey]['samples']) === false) {
+            $this->gauges[$metaKey]['samples'][$valueKey] = 0;
+        }
+        if ($data['command'] === Adapter::COMMAND_SET) {
+            $this->gauges[$metaKey]['samples'][$valueKey] = $data['value'];
+        } else {
+            $this->gauges[$metaKey]['samples'][$valueKey] += $data['value'];
+        }
     }
 
     public function updateCounter(array $data)
     {
-        // TODO: Implement updateCounter() method.
+        $metaKey = $this->metaKey($data);
+        $valueKey = $this->valueKey($data);
+        if (array_key_exists($metaKey, $this->counters) === false) {
+            $this->counters[$metaKey] = [
+                'meta' => $this->metaData($data),
+                'samples' => []
+            ];
+        }
+        if (array_key_exists($valueKey, $this->counters[$metaKey]['samples']) === false) {
+            $this->counters[$metaKey]['samples'][$valueKey] = 0;
+        }
+        if ($data['command'] === Adapter::COMMAND_SET) {
+            $this->counters[$metaKey]['samples'][$valueKey] = 0;
+        } else {
+            $this->counters[$metaKey]['samples'][$valueKey] += $data['value'];
+        }
     }
 
+    /**
+     * @param array $data
+     *
+     * @param       $bucket
+     *
+     * @return string
+     */
+    private function histogramBucketValueKey(array $data, $bucket)
+    {
+        return implode(':', [
+            $data['type'],
+            $data['name'],
+            json_encode($data['labelValues']),
+            $bucket
+        ]);
+    }
 
+    /**
+     * @param array $data
+     *
+     * @return string
+     */
+    private function metaKey(array $data)
+    {
+        return implode(':', [$data['type'], $data['name'], 'meta']);
+    }
+
+    /**
+     * @param array $data
+     *
+     * @return string
+     */
+    private function valueKey(array $data)
+    {
+        return implode(':',
+            [$data['type'], $data['name'], json_encode($data['labelValues']), 'value']);
+    }
+
+    /**
+     * @param array $data
+     *
+     * @return array
+     */
+    private function metaData(array $data)
+    {
+        $metricsMetaData = $data;
+        unset($metricsMetaData['value']);
+        unset($metricsMetaData['command']);
+        unset($metricsMetaData['labelValues']);
+        return $metricsMetaData;
+    }
+
+    private function sortSamples(array &$samples)
+    {
+        usort($samples, function ($a, $b) {
+            return strcmp(implode("", $a['labelValues']), implode("", $b['labelValues']));
+        });
+    }
 }
diff --git a/tests/Test/Prometheus/InMemory/CollectorRegistryTest.php b/tests/Test/Prometheus/InMemory/CollectorRegistryTest.php
new file mode 100644
index 0000000..7309708
--- /dev/null
+++ b/tests/Test/Prometheus/InMemory/CollectorRegistryTest.php
@@ -0,0 +1,16 @@
+<?php
+
+
+namespace Test\Prometheus\InMemory;
+
+use Prometheus\Storage\InMemory;
+use Test\Prometheus\AbstractCollectorRegistryTest;
+
+class CollectorRegistryTest extends AbstractCollectorRegistryTest
+{
+    public function configureAdapter()
+    {
+        $this->adapter = new InMemory();
+        $this->adapter->flushMemory();
+    }
+}
diff --git a/tests/Test/Prometheus/InMemory/CounterTest.php b/tests/Test/Prometheus/InMemory/CounterTest.php
new file mode 100644
index 0000000..03ed614
--- /dev/null
+++ b/tests/Test/Prometheus/InMemory/CounterTest.php
@@ -0,0 +1,20 @@
+<?php
+
+
+namespace Test\Prometheus\InMemory;
+
+use Prometheus\Storage\InMemory;
+use Test\Prometheus\AbstractCounterTest;
+
+/**
+ * See https://prometheus.io/docs/instrumenting/exposition_formats/
+ */
+class CounterTest extends AbstractCounterTest
+{
+
+    public function configureAdapter()
+    {
+        $this->adapter = new InMemory();
+        $this->adapter->flushMemory();
+    }
+}
diff --git a/tests/Test/Prometheus/InMemory/GaugeTest.php b/tests/Test/Prometheus/InMemory/GaugeTest.php
new file mode 100644
index 0000000..75e0f3c
--- /dev/null
+++ b/tests/Test/Prometheus/InMemory/GaugeTest.php
@@ -0,0 +1,20 @@
+<?php
+
+
+namespace Test\Prometheus\InMemory;
+
+use Prometheus\Storage\InMemory;
+use Test\Prometheus\AbstractGaugeTest;
+
+/**
+ * See https://prometheus.io/docs/instrumenting/exposition_formats/
+ */
+class GaugeTest extends AbstractGaugeTest
+{
+
+    public function configureAdapter()
+    {
+        $this->adapter = new InMemory();
+        $this->adapter->flushMemory();
+    }
+}
diff --git a/tests/Test/Prometheus/InMemory/HistogramTest.php b/tests/Test/Prometheus/InMemory/HistogramTest.php
new file mode 100644
index 0000000..283ec3e
--- /dev/null
+++ b/tests/Test/Prometheus/InMemory/HistogramTest.php
@@ -0,0 +1,21 @@
+<?php
+
+
+namespace Test\Prometheus\InMemory;
+
+use Prometheus\Storage\InMemory;
+use Test\Prometheus\AbstractHistogramTest;
+
+/**
+ * See https://prometheus.io/docs/instrumenting/exposition_formats/
+ */
+class HistogramTest extends AbstractHistogramTest
+{
+
+    public function configureAdapter()
+    {
+        $this->adapter = new InMemory();
+        $this->adapter->flushMemory();
+    }
+}
+