diff --git a/impression.go b/impression.go
index 7694f7e..93e6be8 100644
--- a/impression.go
+++ b/impression.go
@@ -36,6 +36,7 @@ type Impression struct {
 	Exp                   int             `json:"exp,omitempty"`               // Advisory as to the number of seconds that may elapse between the auction and the actual impression.
 	IFrameBusters         []string        `json:"iframebuster,omitempty"`      // Array of names for supportediframe busters.
 	Rewarded              int             `json:"rwdd,omitempty"`              // Impression is rewarded, Default: 0 ("1": yes, "0": no)
+	Metric                []Metric        `json:"metric,omitempty"`
 	Ext                   json.RawMessage `json:"ext,omitempty"`
 }
 
diff --git a/metric.go b/metric.go
new file mode 100644
index 0000000..f6171c8
--- /dev/null
+++ b/metric.go
@@ -0,0 +1,48 @@
+package openrtb
+
+import "encoding/json"
+
+// 3.2.5 Object: Metric
+//
+// This object is associated with an impression as an array of metrics.
+// These metrics can offer insight into the impression to assist with decisioning such as average recent viewability, click-through rate, etc.
+// Each metric is identified by its type, reports the value of the metric, and optionally identifies the source or vendor measuring the value.
+type Metric struct {
+
+	// Attribute:
+	//   type
+	// Type:
+	//   string; required
+	// Description:
+	//   Type of metric being presented using exchange curated string
+	//   names which should be published to bidders a priori.
+	Type string `json:"type"`
+
+	// Attribute:
+	//   value
+	// Type:
+	//   float; required
+	// Description:
+	//   Number representing the value of the metric. Probabilities
+	//   must be in the range 0.0 – 1.0.
+	Value float64 `json:"value,omitempty"`
+
+	// Attribute:
+	//   vendor
+	// Type:
+	//   string; recommended
+	// Description:
+	//   Source of the value using exchange curated string names
+	//   which should be published to bidders a priori. If the exchange
+	//   itself is the source versus a third party, “EXCHANGE” is
+	//   recommended.
+	Vendor string `json:"vendor,omitempty"`
+
+	// Attribute:
+	//   ext
+	// Type:
+	//   object
+	// Description:
+	//   Placeholder for exchange-specific extensions to OpenRTB.
+	Ext json.RawMessage `json:"ext,omitempty"`
+}