diff --git a/src/Prometheus/CollectorRegistry.php b/src/Prometheus/CollectorRegistry.php
index 541e1d8..2742ac8 100644
--- a/src/Prometheus/CollectorRegistry.php
+++ b/src/Prometheus/CollectorRegistry.php
@@ -36,6 +36,11 @@ class CollectorRegistry
      */
     private $histograms = [];
 
+    /**
+     * @var Summary[]
+     */
+    private $summaries = [];
+
     /**
      * CollectorRegistry constructor.
      * @param Adapter $redisAdapter
@@ -238,6 +243,66 @@ public function getOrRegisterHistogram($namespace, $name, $help, $labels = [], $
         return $histogram;
     }
 
+    /**
+     * @param string $namespace e.g. cms
+     * @param string $name e.g. duration_seconds
+     * @param string $help e.g. A duration in seconds.
+     * @param array $labels e.g. ['controller', 'action']
+     * @param array $quantiles e.g. [0.1, 0.5, 0.9]
+     * @return Summary
+     * @throws MetricsRegistrationException
+     */
+    public function registerSummary(string $namespace, string $name, string $help, array $labels = [], ?array $quantiles = null): Summary
+    {
+        $metricIdentifier = self::metricIdentifier($namespace, $name);
+        if (isset($this->summaries[$metricIdentifier])) {
+            throw new MetricsRegistrationException("Metric already registered");
+        }
+        $this->summaries[$metricIdentifier] = new Summary(
+            $this->storageAdapter,
+            $namespace,
+            $name,
+            $help,
+            $labels,
+            $quantiles
+        );
+        return $this->summaries[$metricIdentifier];
+    }
+
+    /**
+     * @param string $namespace
+     * @param string $name
+     * @return Summary
+     * @throws MetricNotFoundException
+     */
+    public function getSummary(string $namespace, string $name): Summary
+    {
+        $metricIdentifier = self::metricIdentifier($namespace, $name);
+        if (!isset($this->summaries[$metricIdentifier])) {
+            throw new MetricNotFoundException("Metric not found:" . $metricIdentifier);
+        }
+        return $this->summaries[self::metricIdentifier($namespace, $name)];
+    }
+
+    /**
+     * @param string $namespace e.g. cms
+     * @param string $name e.g. duration_seconds
+     * @param string $help e.g. A duration in seconds.
+     * @param array $labels e.g. ['controller', 'action']
+     * @param array $quantiles e.g. [0.1, 0.5, 0.9]
+     * @return Summary
+     * @throws MetricsRegistrationException
+     */
+    public function getOrRegisterSummary(string $namespace, string $name, string $help, array $labels = [], ?array $quantiles = null): Summary
+    {
+        try {
+            $summary = $this->getSummary($namespace, $name);
+        } catch (MetricNotFoundException $e) {
+            $summary = $this->registerSummary($namespace, $name, $help, $labels, $quantiles);
+        }
+        return $summary;
+    }
+
     /**
      * @param $namespace
      * @param $name
diff --git a/src/Prometheus/Storage/APC.php b/src/Prometheus/Storage/APC.php
index 2fe659d..4598a6d 100644
--- a/src/Prometheus/Storage/APC.php
+++ b/src/Prometheus/Storage/APC.php
@@ -59,6 +59,14 @@ public function updateHistogram(array $data): void
         apcu_inc($this->histogramBucketValueKey($data, $bucketToIncrease));
     }
 
+    /**
+     * @param array $data
+     */
+    public function updateSummary(array $data)
+    {
+        // TODO: Implement updateSummary() method.
+    }
+
     /**
      * @param array $data
      */
diff --git a/src/Prometheus/Storage/Adapter.php b/src/Prometheus/Storage/Adapter.php
index 068e1d9..ceb4230 100644
--- a/src/Prometheus/Storage/Adapter.php
+++ b/src/Prometheus/Storage/Adapter.php
@@ -23,6 +23,12 @@ public function collect();
      */
     public function updateHistogram(array $data): void;
 
+    /**
+     * @param array $data
+     * @return void
+     */
+    public function updateSummary(array $data): void;
+
     /**
      * @param array $data
      * @return void
diff --git a/src/Prometheus/Storage/InMemory.php b/src/Prometheus/Storage/InMemory.php
index bfd4c70..a64e4b2 100644
--- a/src/Prometheus/Storage/InMemory.php
+++ b/src/Prometheus/Storage/InMemory.php
@@ -175,6 +175,15 @@ public function updateHistogram(array $data): void
         $this->histograms[$metaKey]['samples'][$bucketKey] += 1;
     }
 
+    /**
+     * @param array $data
+     * @return void
+     */
+    public function updateSummary(array $data): void
+    {
+        // TODO: Implement updateSummary() method.
+    }
+
     /**
      * @param array $data
      */
diff --git a/src/Prometheus/Storage/Redis.php b/src/Prometheus/Storage/Redis.php
index 85e3000..0b49aea 100644
--- a/src/Prometheus/Storage/Redis.php
+++ b/src/Prometheus/Storage/Redis.php
@@ -10,6 +10,7 @@
 use Prometheus\Gauge;
 use Prometheus\Histogram;
 use Prometheus\MetricFamilySamples;
+use Prometheus\Summary;
 
 class Redis implements Adapter
 {
@@ -105,6 +106,7 @@ public function collect(): array
         $metrics = $this->collectHistograms();
         $metrics = array_merge($metrics, $this->collectGauges());
         $metrics = array_merge($metrics, $this->collectCounters());
+        $metrics = array_merge($metrics, $this->collectSummaries());
         return array_map(
             function (array $metric) {
                 return new MetricFamilySamples($metric);
@@ -198,6 +200,47 @@ public function updateHistogram(array $data): void
         );
     }
 
+    /**
+     * @param array $data
+     * @throws StorageException
+     */
+    public function updateSummary(array $data): void
+    {
+        $this->openConnection();
+        $metaData = $data;
+        unset($metaData['value']);
+        unset($metaData['labelValues']);
+        $this->redis->eval(
+            <<<LUA
+local increment = redis.call('hIncrByFloat', KEYS[1], KEYS[2], ARGV[1])
+redis.call('hIncrBy', KEYS[1], KEYS[3], 1)
+local values = redis.call('hGet', KEYS[1], KEYS[4])
+if values == false then
+  values = ARGV[1]
+else
+  values = values .. "," .. ARGV[1]
+end
+redis.call('hSet', KEYS[1], KEYS[4], values)
+if increment == ARGV[1] then
+    redis.call('hSet', KEYS[1], '__meta', ARGV[2])
+    redis.call('sAdd', KEYS[5], KEYS[1])
+end
+LUA
+            ,
+            [
+                $this->toMetricKey($data),
+                json_encode(['b' => 'sum', 'labelValues' => $data['labelValues']]),
+                json_encode(['b' => 'count', 'labelValues' => $data['labelValues']]),
+                json_encode(['b' => 'values', 'labelValues' => $data['labelValues']]),
+                self::$prefix . Summary::TYPE . self::PROMETHEUS_METRIC_KEYS_SUFFIX,
+                $data['value'],
+                json_encode($metaData),
+            ],
+            5
+        );
+    }
+
+
     /**
      * @param array $data
      * @throws StorageException
@@ -348,6 +391,66 @@ private function collectHistograms(): array
         return $histograms;
     }
 
+    /**
+     * @return array
+     */
+    private function collectSummaries(): array
+    {
+        $keys = $this->redis->sMembers(self::$prefix . Summary::TYPE . self::PROMETHEUS_METRIC_KEYS_SUFFIX);
+        sort($keys);
+        $summaries = [];
+
+        foreach ($keys as $key) {
+            $raw = $this->redis->hGetAll($key);
+            $summary = json_decode($raw['__meta'], true);
+            unset($raw['__meta']);
+            $allLabelValues = [];
+
+            foreach (array_keys($raw) as $k) {
+                $d = json_decode($k, true);
+                $allLabelValues[] = $d['labelValues'];
+            }
+
+            // We need set semantics.
+            // This is the equivalent of array_unique but for arrays of arrays.
+            $allLabelValues = array_map('unserialize', array_unique(array_map('serialize', $allLabelValues)));
+            sort($allLabelValues);
+
+            foreach ($allLabelValues as $labelValues) {
+                $valuesKey = json_encode(['b' => 'values', 'labelValues' => $labelValues]);
+                $values = !empty($raw[$valuesKey]) ? explode(',', $raw[$valuesKey]) : [];
+                foreach ($summary['quantiles'] as $quantile) {
+                    $summary['samples'][] = [
+                        'name' => $summary['name'],
+                        'labelNames' => ['quantile'],
+                        'labelValues' => array_merge($labelValues, ['quantile' => $quantile]),
+                        'value' => Summary::getQuantile($quantile, $values)
+                    ];
+                }
+
+                // Add the count
+                $countKey = json_encode(['b' => 'count', 'labelValues' => $labelValues]);
+                $summary['samples'][] = [
+                    'name' => $summary['name'] . '_count',
+                    'labelNames' => [],
+                    'labelValues' => $labelValues,
+                    'value' => !empty($raw[$countKey]) ? (int)$raw[$countKey] : 0,
+                ];
+
+                // Add the sum
+                $sumKey = json_encode(['b' => 'sum', 'labelValues' => $labelValues]);
+                $summary['samples'][] = [
+                    'name' => $summary['name'] . '_sum',
+                    'labelNames' => [],
+                    'labelValues' => $labelValues,
+                    'value' => !empty($raw[$sumKey]) ? $raw[$sumKey] : 0,
+                ];
+            }
+            $summaries[] = $summary;
+        }
+        return $summaries;
+    }
+
     /**
      * @return array
      */
diff --git a/src/Prometheus/Summary.php b/src/Prometheus/Summary.php
new file mode 100644
index 0000000..7a2166c
--- /dev/null
+++ b/src/Prometheus/Summary.php
@@ -0,0 +1,108 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Prometheus;
+
+use InvalidArgumentException;
+use Prometheus\Storage\Adapter;
+
+class Summary extends Collector
+{
+    const TYPE = 'summary';
+
+    /**
+     * @var array|null
+     */
+    private $quantiles;
+
+    /**
+     * @param Adapter $adapter
+     * @param string $namespace
+     * @param string $name
+     * @param string $help
+     * @param array $labels
+     * @param array $quantiles
+     * @throws InvalidArgumentException
+     */
+    public function __construct(Adapter $adapter, string $namespace, string $name, string $help, array $labels = [], ?array $quantiles = null)
+    {
+        parent::__construct($adapter, $namespace, $name, $help, $labels);
+
+        if (null === $quantiles) {
+            $quantiles = self::getDefaultQuantiles();
+        }
+
+        if (0 === count($quantiles)) {
+            throw new InvalidArgumentException('Summary must have at least one quantile.');
+        }
+
+        for ($i = 0; $i < count($quantiles) - 1; $i++) {
+            if ($quantiles[$i] >= $quantiles[$i + 1]) {
+                throw new InvalidArgumentException(
+                    'Summary quantiles must be in increasing order: ' .
+                    $quantiles[$i] . ' >= ' . $quantiles[$i + 1]
+                );
+            }
+        }
+        foreach ($labels as $label) {
+            if ($label === 'quantile') {
+                throw new InvalidArgumentException('Summary cannot have a label named "quantile".');
+            }
+        }
+        $this->quantiles = $quantiles;
+    }
+
+    /**
+     * List of default quantiles
+     * @return array
+     */
+    public static function getDefaultQuantiles(): array
+    {
+        return [
+            0.01, 0.05, 0.5, 0.9, 0.99,
+        ];
+    }
+
+    /**
+     * @param double $value e.g. 123
+     * @param array $labels e.g. ['status', 'opcode']
+     */
+    public function observe(float $value, array $labels = []): void
+    {
+        $this->assertLabelsAreDefinedCorrectly($labels);
+        $this->storageAdapter->updateSummary(
+            [
+                'value' => $value,
+                'name' => $this->getName(),
+                'help' => $this->getHelp(),
+                'type' => $this->getType(),
+                'labelNames' => $this->getLabelNames(),
+                'labelValues' => $labels,
+                'quantiles' => $this->quantiles,
+            ]
+        );
+    }
+
+    /**
+     * @param float $percentile
+     * @param array $values
+     * @return float
+     */
+    public static function getQuantile(float $percentile, array $values): float
+    {
+        sort($values);
+        $index = (int)($percentile * count($values));
+        return (floor($index) === $index)
+            ? ($values[$index - 1] + $values[$index]) / 2
+            : (float) $values[(int)floor($index)];
+    }
+
+    /**
+     * @return string
+     */
+    public function getType(): string
+    {
+        return self::TYPE;
+    }
+}