diff --git a/impression.go b/impression.go
index eeaee85..589daf6 100644
--- a/impression.go
+++ b/impression.go
@@ -32,8 +32,9 @@ type Impression struct {
 	BidFloor              float64         `json:"bidfloor,omitempty"`          // Bid floor for this impression in CPM
 	BidFloorCurrency      string          `json:"bidfloorcur,omitempty"`       // Currency of bid floor
 	Secure                NumberOrString  `json:"secure,omitempty"`            // Flag to indicate whether the impression requires secure HTTPS URL creative assets and markup.
-	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.
+	Quantity              *Quantity       `json:"qty,omitempty"`          // Includes the impression multiplier, and describes its source.
+	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.
 	Ext                   json.RawMessage `json:"ext,omitempty"`
 }
 
@@ -66,6 +67,11 @@ func (imp *Impression) Validate() error {
 			return err
 		}
 	}
+	if imp.Quantity != nil {
+		if err := imp.Quantity.Validate(); err != nil {
+			return err
+		}
+	}
 
 	return nil
 }
diff --git a/impression_test.go b/impression_test.go
index 958816d..95046a3 100644
--- a/impression_test.go
+++ b/impression_test.go
@@ -31,6 +31,9 @@ func TestImpression(t *testing.T) {
 				},
 			},
 		},
+		Quantity: &Quantity{
+			Multiplier: 1.0,
+		},
 	}
 	if got := subject; !reflect.DeepEqual(exp, got) {
 		t.Errorf("expected %+v, got %+v", exp, got)
diff --git a/quantity.go b/quantity.go
new file mode 100644
index 0000000..9ec3fee
--- /dev/null
+++ b/quantity.go
@@ -0,0 +1,37 @@
+package openrtb
+
+import (
+	"encoding/json"
+	"errors"
+)
+
+var (
+	ErrMissingMultiplier        = errors.New("openrtb: qty.multiplier is required")
+	ErrMissingMeasurementVendor = errors.New("openrtb: qty.vendor is required when qty.sourcetype is 1 (Measurement Vendor)")
+)
+
+type MeasurementSourceType int
+
+const (
+	MeasurementSourceTypeUnknown           MeasurementSourceType = 0
+	MeasurementSourceTypeMeasurementVendor MeasurementSourceType = 1
+	MeasurementSourceTypePublisher         MeasurementSourceType = 2
+	MeasurementSourceTypeExchange          MeasurementSourceType = 3
+)
+
+type Quantity struct {
+	Multiplier float64               `json:"multiplier"`
+	SourceType MeasurementSourceType `json:"sourcetype,omitempty"`
+	Vendor     string                `json:"vendor,omitempty"`
+	Ext        *json.RawMessage       `json:"ext,omitempty"`
+}
+
+func (qty *Quantity) Validate() error {
+	if qty.Multiplier == 0 {
+		return ErrMissingMultiplier
+	}
+	if qty.SourceType == MeasurementSourceTypeMeasurementVendor && qty.Vendor == "" {
+		return ErrMissingMeasurementVendor
+	}
+	return nil
+}
diff --git a/quantity_test.go b/quantity_test.go
new file mode 100644
index 0000000..2206437
--- /dev/null
+++ b/quantity_test.go
@@ -0,0 +1,55 @@
+package openrtb_test
+
+import (
+	"reflect"
+	"testing"
+
+	. "github.com/bsm/openrtb/v3"
+)
+
+func TestQuantity(t *testing.T) {
+	var subject *Quantity
+	if err := fixture("quantity", &subject); err != nil {
+		t.Fatalf("expected no error, got %+v", err)
+	}
+
+	exp := &Quantity{
+		Multiplier: 3.14,
+		SourceType: MeasurementSourceTypePublisher,
+	}
+
+	if !reflect.DeepEqual(exp, subject) {
+		t.Fatalf("expected %+v, got %+v", exp, subject)
+	}
+}
+
+func TestQuantity_Validate(t *testing.T) {
+	subject := Quantity{}
+	if got := subject.Validate(); got != ErrMissingMultiplier {
+		t.Fatalf("expected %+v, got %+v", ErrMissingMultiplier, got)
+	}
+
+	// If MeasurementSourceType is MeasurementSourceTypeMeasurementVendor, the
+	// Vendor field should not be empty.
+	subject = Quantity{
+		Multiplier: 1.0,
+		SourceType: MeasurementSourceTypeMeasurementVendor,
+	}
+	if got := subject.Validate(); got != ErrMissingMeasurementVendor {
+		t.Fatalf("expected %+v, got %+v", ErrMissingMeasurementVendor, got)
+	}
+
+	subject.Vendor = "TestVendor" // Should fix the invalid Quantity
+	if got := subject.Validate(); got != nil {
+		t.Fatalf("expected no error, got %+v", got)
+	}
+
+	// All other value from MeasurementSourceType can be used without Vendor
+	subject = Quantity{
+		Multiplier: 2.0,
+		SourceType: MeasurementSourceTypeUnknown,
+	}
+	if got := subject.Validate(); got != nil {
+		t.Fatalf("expected nil, got %+v", got)
+	}
+}
diff --git a/testdata/impression.json b/testdata/impression.json
index a66434d..3d1bd45 100644
--- a/testdata/impression.json
+++ b/testdata/impression.json
@@ -15,5 +15,8 @@
         "at": 2
       }
     ]
+  },
+  "qty": {
+    "multiplier": 1.0
   }
 }
diff --git a/testdata/quantity.json b/testdata/quantity.json
new file mode 100644
index 0000000..1d03a4e
--- /dev/null
+++ b/testdata/quantity.json
@@ -0,0 +1,4 @@
+{
+  "multiplier": 3.14,
+  "sourcetype": 2
+}