diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3c86bcce8..fcfcefd7b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # 12.0.0, in progress
 
+## Added
+
+* The OpenTracing implementation's `Tracer.Inject` in the `trace` package now sets HTTP headers in a way that tools like [Envoy](https://www.envoyproxy.io/) can propagate on traces. Thanks, [antifuchs](https://github.com/antifuchs)!
+
 ## Bugfixes
 * The signalfx client no longer reports a timeout when submission to the datapoint API endpoint encounters an error. Thanks, [antifuchs](https://github.com/antifuchs)!
 
diff --git a/http/http.go b/http/http.go
index 184066ae4..dbadde433 100644
--- a/http/http.go
+++ b/http/http.go
@@ -131,6 +131,9 @@ func (tripper *TraceRoundTripper) RoundTrip(req *http.Request) (*http.Response,
 	span.SetTag("action", tripper.prefix)
 	defer span.ClientFinish(tripper.tc)
 
+	// Add OpenTracing headers to the request, so downstream reqs can be identified:
+	trace.GlobalTracer.InjectRequest(span.Trace, req)
+
 	hct := newHTTPClientTracer(span.Attach(req.Context()), tripper.tc, tripper.prefix)
 	req = req.WithContext(httptrace.WithClientTrace(req.Context(), hct.getClientTrace()))
 	defer hct.finishSpan()
diff --git a/trace/opentracing.go b/trace/opentracing.go
index 1ad056980..0659787e1 100644
--- a/trace/opentracing.go
+++ b/trace/opentracing.go
@@ -20,9 +20,10 @@ import (
 
 // Lists the names of headers that a specification uses for representing trace information.
 type HeaderGroup struct {
-	TraceID   string
-	SpanID    string
-	numFormat headerGroupNumFormat
+	TraceID         string
+	SpanID          string
+	numFormat       headerGroupNumFormat
+	OutgoingHeaders map[string]string
 }
 
 type headerGroupNumFormat int
@@ -42,6 +43,9 @@ var HeaderFormats = []HeaderGroup{
 		TraceID:   "ot-tracer-traceid",
 		SpanID:    "ot-tracer-spanid",
 		numFormat: hexadecimal,
+		OutgoingHeaders: map[string]string{
+			"ot-tracer-sampled": "true",
+		},
 	},
 	// OpenTracing format.
 	HeaderGroup{
@@ -60,6 +64,10 @@ var HeaderFormats = []HeaderGroup{
 	},
 }
 
+// defaultHeaderFormat is the way .Inject sets HTTP headers by
+// default.
+var defaultHeaderFormat = HeaderFormats[0]
+
 // GlobalTracer is the… global tracer!
 var GlobalTracer = Tracer{}
 
@@ -514,7 +522,6 @@ func (tracer Tracer) ExtractRequestChild(resource string, req *http.Request, nam
 // Inject injects the provided SpanContext into the carrier for propagation.
 // It will return opentracing.ErrUnsupportedFormat if the format is not supported.
 // TODO support other SpanContext implementations
-// TODO support all the BuiltinFormats
 func (t Tracer) Inject(sm opentracing.SpanContext, format interface{}, carrier interface{}) (err error) {
 	defer func() {
 		if r := recover(); r != nil {
@@ -528,7 +535,8 @@ func (t Tracer) Inject(sm opentracing.SpanContext, format interface{}, carrier i
 		return ErrUnsupportedSpanContext
 	}
 
-	if format == opentracing.Binary {
+	switch format {
+	case opentracing.Binary:
 		// carrier is guaranteed to be an io.Writer by contract
 		w := carrier.(io.Writer)
 
@@ -541,6 +549,20 @@ func (t Tracer) Inject(sm opentracing.SpanContext, format interface{}, carrier i
 		}
 
 		return trace.ProtoMarshalTo(w)
+	case opentracing.HTTPHeaders:
+		h := carrier.(opentracing.HTTPHeadersCarrier)
+		base := 10
+		if defaultHeaderFormat.numFormat == hexadecimal {
+			base = 16
+		}
+		h.Set(defaultHeaderFormat.SpanID, strconv.FormatInt(sc.SpanID(), base))
+		h.Set(defaultHeaderFormat.TraceID, strconv.FormatInt(sc.TraceID(), base))
+		if defaultHeaderFormat.OutgoingHeaders != nil {
+			for name, value := range defaultHeaderFormat.OutgoingHeaders {
+				h.Set(name, value)
+			}
+		}
+		return nil
 	}
 
 	// If the carrier is a TextMapWriter, treat it as one, regardless of what the format is
diff --git a/trace/opentracing_test.go b/trace/opentracing_test.go
index 1b5cbf3b2..5b455bd83 100644
--- a/trace/opentracing_test.go
+++ b/trace/opentracing_test.go
@@ -222,6 +222,11 @@ func TestTracerInjectExtractHeader(t *testing.T) {
 	err = tracer.Inject(trace.context(), opentracing.HTTPHeaders, carrier)
 	assert.NoError(t, err)
 
+	assert.NotEqual(t, "", req.Header.Get(defaultHeaderFormat.SpanID),
+		"Headers %v should contain %q", req.Header, defaultHeaderFormat.SpanID)
+	assert.NotEqual(t, "", req.Header.Get(defaultHeaderFormat.TraceID),
+		"Headers %v should contain %q", req.Header, defaultHeaderFormat.TraceID)
+
 	c, err := tracer.Extract(opentracing.HTTPHeaders, carrier)
 	assert.NoError(t, err)
 
@@ -230,7 +235,6 @@ func TestTracerInjectExtractHeader(t *testing.T) {
 	assert.Equal(t, trace.TraceID, ctx.TraceID())
 
 	assert.Equal(t, trace.SpanID, ctx.SpanID(), "original trace and context should share the same SpanId")
-	assert.Equal(t, trace.Resource, ctx.Resource())
 }
 
 func TestTraceExtractHeaderEnvoy(t *testing.T) {