diff --git a/.circleci/config.yml b/.circleci/config.yml
index 46a9d1f..ee250fb 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -7,13 +7,20 @@ jobs:
       - checkout
       - run: ./ci/install_dependencies.sh
       - run: ./ci/do_ci.sh cmake.asan
+      - store_artifacts:
+          path: /build/Testing/Temporary/LastTest.log
+          destination: Test.log
   tsan:
     docker:
       - image: ubuntu:17.10
     steps:
       - checkout
+      - run: mkdir -p /build
       - run: ./ci/install_dependencies.sh
-      - run: ./ci/do_ci.sh cmake.tsan
+      - run: BUILD_DIR=/build ./ci/do_ci.sh cmake.tsan
+      - store_artifacts:
+          path: /build/Testing/Temporary/LastTest.log
+          destination: Test.log
   bazel:
     docker:
       - image: ubuntu:17.10
diff --git a/.gitignore b/.gitignore
index 6fc863d..87b0eb5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -32,3 +32,5 @@
 *.app
 
 bazel-*
+
+.build/
diff --git a/zipkin/include/zipkin/span_context.h b/zipkin/include/zipkin/span_context.h
index 04816e0..48c08f5 100644
--- a/zipkin/include/zipkin/span_context.h
+++ b/zipkin/include/zipkin/span_context.h
@@ -58,6 +58,8 @@ class SpanContext {
       : trace_id_{trace_id}, id_{id}, parent_id_{parent_id}, flags_{flags},
         is_initialized_{true} {}
 
+  bool isSampled() const { return flags_ & zipkin::sampled_flag; }
+
   /**
    * @return the span id as an integer
    */
diff --git a/zipkin/include/zipkin/zipkin_core_types.h b/zipkin/include/zipkin/zipkin_core_types.h
index 04b275f..510a0d9 100644
--- a/zipkin/include/zipkin/zipkin_core_types.h
+++ b/zipkin/include/zipkin/zipkin_core_types.h
@@ -332,6 +332,9 @@ class Span : public ZipkinBase {
       : trace_id_(0), name_(), id_(0), debug_(false), monotonic_start_time_(0),
         tracer_(nullptr) {}
 
+  void setSampled(const bool val) { sampled_ = val; }
+  bool isSampled() const { return sampled_; }
+
   /**
    * Sets the span's trace id attribute.
    */
@@ -566,6 +569,7 @@ class Span : public ZipkinBase {
   std::string name_;
   uint64_t id_;
   Optional<TraceId> parent_id_;
+  bool sampled_{true};
   bool debug_;
   std::vector<Annotation> annotations_;
   std::vector<BinaryAnnotation> binary_annotations_;
diff --git a/zipkin/src/span_context.cc b/zipkin/src/span_context.cc
index b5954e6..28c148c 100644
--- a/zipkin/src/span_context.cc
+++ b/zipkin/src/span_context.cc
@@ -8,6 +8,11 @@ SpanContext::SpanContext(const Span &span) {
   trace_id_ = span.traceId();
   id_ = span.id();
   parent_id_ = span.isSetParentId() ? span.parentId() : 0;
+  flags_ = 0;
+
+  if (span.isSampled()) {
+    flags_ |= static_cast<unsigned char>(zipkin::sampled_flag);
+  }
 
   for (const Annotation &annotation : span.annotations()) {
     if (annotation.value() == ZipkinCoreConstants::get().CLIENT_RECV) {
diff --git a/zipkin/src/zipkin_core_types.cc b/zipkin/src/zipkin_core_types.cc
index 94a8221..b7ae704 100644
--- a/zipkin/src/zipkin_core_types.cc
+++ b/zipkin/src/zipkin_core_types.cc
@@ -185,7 +185,9 @@ const std::string Span::toJson() {
 
 void Span::finish() {
   if (auto t = tracer()) {
-    t->reportSpan(std::move(*this));
+    if (this->isSampled()) {
+      t->reportSpan(std::move(*this));
+    }
   }
 }
 
diff --git a/zipkin_opentracing/CMakeLists.txt b/zipkin_opentracing/CMakeLists.txt
index 93b582c..723ea5d 100644
--- a/zipkin_opentracing/CMakeLists.txt
+++ b/zipkin_opentracing/CMakeLists.txt
@@ -8,7 +8,8 @@ set(ZIPKIN_OPENTRACING_SRCS src/utility.cc
                             src/propagation.cc
                             src/dynamic_load.cc
                             src/tracer_factory.cc
-                            src/opentracing.cc)
+                            src/opentracing.cc
+                            src/sampling.cc)
 
 if (BUILD_SHARED_LIBS)               
   add_library(zipkin_opentracing SHARED ${ZIPKIN_OPENTRACING_SRCS})
diff --git a/zipkin_opentracing/example/text_map_carrier.h b/zipkin_opentracing/example/text_map_carrier.h
index 1ff45b3..fa0a5d9 100644
--- a/zipkin_opentracing/example/text_map_carrier.h
+++ b/zipkin_opentracing/example/text_map_carrier.h
@@ -5,10 +5,10 @@
 #include <string>
 #include <unordered_map>
 
-using opentracing::TextMapReader;
-using opentracing::TextMapWriter;
 using opentracing::expected;
 using opentracing::string_view;
+using opentracing::TextMapReader;
+using opentracing::TextMapWriter;
 
 class TextMapCarrier : public TextMapReader, public TextMapWriter {
 public:
diff --git a/zipkin_opentracing/include/zipkin/opentracing.h b/zipkin_opentracing/include/zipkin/opentracing.h
index 8c869dd..e4f012a 100644
--- a/zipkin_opentracing/include/zipkin/opentracing.h
+++ b/zipkin_opentracing/include/zipkin/opentracing.h
@@ -8,6 +8,7 @@ struct ZipkinOtTracerOptions {
   uint32_t collector_port = 9411;
   SteadyClock::duration reporting_period = DEFAULT_REPORTING_PERIOD;
   size_t max_buffered_spans = DEFAULT_SPAN_BUFFER_SIZE;
+  double sample_rate = 1.0;
 
   std::string service_name;
   IpAddress service_address;
@@ -19,4 +20,5 @@ makeZipkinOtTracer(const ZipkinOtTracerOptions &options);
 std::shared_ptr<opentracing::Tracer>
 makeZipkinOtTracer(const ZipkinOtTracerOptions &options,
                    std::unique_ptr<Reporter> &&reporter);
+
 } // namespace zipkin
diff --git a/zipkin_opentracing/src/opentracing.cc b/zipkin_opentracing/src/opentracing.cc
index 771c331..ac4e05d 100644
--- a/zipkin_opentracing/src/opentracing.cc
+++ b/zipkin_opentracing/src/opentracing.cc
@@ -1,19 +1,22 @@
+#include <opentracing/util.h>
 #include <zipkin/opentracing.h>
 
 #include "propagation.h"
+#include "sampling.h"
 #include "utility.h"
 #include <atomic>
 #include <cstring>
 #include <mutex>
+#include <random>
 #include <unordered_map>
 #include <zipkin/tracer.h>
 #include <zipkin/utility.h>
 #include <zipkin/zipkin_core_types.h>
 
-using opentracing::Value;
 using opentracing::expected;
 using opentracing::make_unexpected;
 using opentracing::string_view;
+using opentracing::Value;
 
 namespace ot = opentracing;
 
@@ -99,6 +102,12 @@ class OtSpanContext : public ot::SpanContext {
     return injectSpanContext(writer, span_context_, baggage_);
   }
 
+  bool isSampled() const { return span_context_.isSampled(); }
+
+  bool isValid() const {
+    return span_context_.id() != 0 && !span_context_.trace_id().empty();
+  }
+
 private:
   zipkin::SpanContext span_context_;
   mutable std::mutex baggage_mutex_;
@@ -271,17 +280,29 @@ class OtSpan : public ot::Span {
 class OtTracer : public ot::Tracer,
                  public std::enable_shared_from_this<OtTracer> {
 public:
-  explicit OtTracer(TracerPtr &&tracer) : tracer_{std::move(tracer)} {}
+  explicit OtTracer(TracerPtr &&tracer)
+      : tracer_{std::move(tracer)}, sampler_{new ProbabilisticSampler(1.0)} {}
+  explicit OtTracer(TracerPtr &&tracer, SamplerPtr &&sampler)
+      : tracer_{std::move(tracer)}, sampler_{std::move(sampler)} {}
 
   std::unique_ptr<ot::Span>
   StartSpanWithOptions(string_view operation_name,
                        const ot::StartSpanOptions &options) const
       noexcept override {
+
     // Create the core zipkin span.
     SpanPtr span{new zipkin::Span{}};
     span->setName(operation_name);
     span->setTracer(tracer_.get());
 
+    auto parent = findSpanContext(options.references);
+
+    if (parent && parent->isValid()) {
+      span->setSampled(parent->isSampled());
+    } else {
+      span->setSampled(sampler_->ShouldSample());
+    }
+
     Endpoint endpoint{tracer_->serviceName(), tracer_->address()};
 
     // Add a binary annotation for the serviceName.
@@ -329,6 +350,7 @@ class OtTracer : public ot::Tracer,
 
 private:
   TracerPtr tracer_;
+  SamplerPtr sampler_;
 
   template <class Carrier>
   expected<void> InjectImpl(const ot::SpanContext &sc, Carrier &writer) const
@@ -368,7 +390,8 @@ makeZipkinOtTracer(const ZipkinOtTracerOptions &options,
                    std::unique_ptr<Reporter> &&reporter) {
   TracerPtr tracer{new Tracer{options.service_name, options.service_address}};
   tracer->setReporter(std::move(reporter));
-  return std::shared_ptr<ot::Tracer>{new OtTracer{std::move(tracer)}};
+  SamplerPtr sampler{new ProbabilisticSampler{options.sample_rate}};
+  return std::make_shared<OtTracer>(std::move(tracer), std::move(sampler));
 }
 
 std::shared_ptr<ot::Tracer>
diff --git a/zipkin_opentracing/src/propagation.cc b/zipkin_opentracing/src/propagation.cc
index 1eb5aae..29fb734 100644
--- a/zipkin_opentracing/src/propagation.cc
+++ b/zipkin_opentracing/src/propagation.cc
@@ -64,7 +64,7 @@ injectSpanContext(const opentracing::TextMapWriter &carrier,
   if (!result) {
     return result;
   }
-  result = carrier.Set(zipkin_sampled, "1");
+  result = carrier.Set(zipkin_sampled, span_context.isSampled() ? "1" : "0");
   if (!result) {
     return result;
   }
@@ -135,7 +135,9 @@ extractSpanContext(const opentracing::TextMapReader &carrier,
           if (!parseBool(value, sampled)) {
             return ot::make_unexpected(ot::span_context_corrupted_error);
           }
-          flags |= sampled_flag;
+          if (sampled) {
+            flags |= sampled_flag;
+          }
         } else if (keyCompare(key, zipkin_parent_span_id)) {
           parent_id = Hex::hexToTraceId(value);
           if (!parent_id.valid()) {
diff --git a/zipkin_opentracing/src/sampling.cc b/zipkin_opentracing/src/sampling.cc
new file mode 100644
index 0000000..309e964
--- /dev/null
+++ b/zipkin_opentracing/src/sampling.cc
@@ -0,0 +1,10 @@
+#include "sampling.h"
+#include <random>
+
+namespace zipkin {
+bool ProbabilisticSampler::ShouldSample() {
+  static thread_local std::mt19937 rng(std::random_device{}());
+  std::bernoulli_distribution dist(sample_rate_);
+  return dist(rng);
+}
+} // namespace zipkin
\ No newline at end of file
diff --git a/zipkin_opentracing/src/sampling.h b/zipkin_opentracing/src/sampling.h
new file mode 100644
index 0000000..770cc40
--- /dev/null
+++ b/zipkin_opentracing/src/sampling.h
@@ -0,0 +1,23 @@
+#pragma once
+#include <algorithm>
+#include <memory>
+
+namespace zipkin {
+class Sampler {
+public:
+  virtual ~Sampler() = default;
+  virtual bool ShouldSample() = 0;
+};
+
+class ProbabilisticSampler : public Sampler {
+public:
+  explicit ProbabilisticSampler(double sample_rate)
+      : sample_rate_(std::max(0.0, std::min(sample_rate, 1.0))){};
+  bool ShouldSample() override;
+
+private:
+  double sample_rate_;
+};
+
+typedef std::unique_ptr<Sampler> SamplerPtr;
+} // namespace zipkin
\ No newline at end of file
diff --git a/zipkin_opentracing/src/tracer_factory.cc b/zipkin_opentracing/src/tracer_factory.cc
index 34cb39f..d1f2a02 100644
--- a/zipkin_opentracing/src/tracer_factory.cc
+++ b/zipkin_opentracing/src/tracer_factory.cc
@@ -37,6 +37,11 @@ const char *const configuration_schema = R"(
       "description":
         "The maximum number of spans to buffer before sending them to the collector",
       "minimum": 1
+    },
+    "sample_rate": {
+      "type": "float",
+      "minimum": 0.0,
+      "maxiumum": 1.0
     }
   }
 }
@@ -91,6 +96,9 @@ OtTracerFactory::MakeTracer(const char *configuration,
   if (document.HasMember("max_buffered_spans")) {
     options.max_buffered_spans = document["max_buffered_spans"].GetInt();
   }
+  if (document.HasMember("sample_rate")) {
+    options.sample_rate = document["sample_rate"].GetDouble();
+  }
   return makeZipkinOtTracer(options);
 } catch (const std::bad_alloc &) {
   return opentracing::make_unexpected(
diff --git a/zipkin_opentracing/test/ot_tracer_test.cc b/zipkin_opentracing/test/ot_tracer_test.cc
index bfddf78..4a0868f 100644
--- a/zipkin_opentracing/test/ot_tracer_test.cc
+++ b/zipkin_opentracing/test/ot_tracer_test.cc
@@ -1,3 +1,4 @@
+#include "../src/sampling.h"
 #include "../src/utility.h"
 #include "in_memory_reporter.h"
 #include <algorithm>
@@ -55,6 +56,45 @@ TEST_CASE("ot_tracer") {
     CHECK(hasTag(span, "xyz", true));
   }
 
+  SECTION("Uses sampling rate to determine whether to sample a span.") {
+    auto r = new InMemoryReporter();
+
+    ZipkinOtTracerOptions options;
+    options.sample_rate = 0.0;
+    auto t = makeZipkinOtTracer(options, std::unique_ptr<Reporter>(r));
+
+    auto span_a = t->StartSpan("a");
+    CHECK(span_a);
+    span_a->Finish();
+
+    CHECK(r->spans().empty());
+  }
+
+  SECTION("Propagates sampling decision to child span") {
+    ZipkinOtTracerOptions no_sampling;
+    no_sampling.sample_rate = 0.0;
+    auto r1 = new InMemoryReporter();
+    auto no_sampling_tracer =
+        makeZipkinOtTracer(no_sampling, std::unique_ptr<Reporter>(r1));
+
+    ZipkinOtTracerOptions always_sample;
+    always_sample.sample_rate = 1.0;
+    auto r2 = new InMemoryReporter();
+    auto sampling_tracer =
+        makeZipkinOtTracer(always_sample, std::unique_ptr<Reporter>(r2));
+
+    auto span_a = no_sampling_tracer->StartSpan("a");
+    CHECK(span_a);
+    span_a->Finish();
+    auto span_b =
+        sampling_tracer->StartSpan("b", {ChildOf(&span_a->context())});
+    CHECK(span_b);
+    span_b->Finish();
+
+    CHECK(r1->spans().empty());
+    CHECK(r2->spans().empty());
+  }
+
   SECTION("You can set a single child-of reference when starting a span.") {
     auto span_a = tracer->StartSpan("a");
     CHECK(span_a);