diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4ff7864..50f63d5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,7 +6,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## v0.16.0
 ### Added
-- The tracer now supports B3 context propagation. Propagation can be set by using the `propagator` keyword argument to `Tracer#configure`. Valid values are `:lightstep` (default), and `:b3`.
+- The tracer now supports B3 context propagation. Propagation can be set by using the `propagator` keyword argument to `LightStep.configure`. Valid values are `:lightstep` (default), and `:b3`.
 
 ## v0.15.0
 ### Added
diff --git a/README.md b/README.md
index ef0cfdb..3e32962 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,9 @@ Or install it yourself as:
     # Initialize the singleton tracer
     LightStep.configure(component_name: 'lightstep/ruby/example', access_token: 'your_access_token')
 
+    # Specify a propagation format (options are :lightstep (default) and :b3)
+    LightStep.configure(component_name: 'lightstep/ruby/example', access_token: 'your_access_token', propagator: :b3)
+
     # Create a basic span and attach a log to the span
     span = LightStep.start_span('my_span')
     span.log(event: 'hello world', count: 42)
diff --git a/lib/lightstep/span.rb b/lib/lightstep/span.rb
index ab50c8e..14679eb 100644
--- a/lib/lightstep/span.rb
+++ b/lib/lightstep/span.rb
@@ -56,7 +56,7 @@ def initialize(
       ref = ref.context if (Span === ref)
 
       if SpanContext === ref
-        @context = SpanContext.new(id: LightStep.guid, trace_id: ref.trace_id)
+        @context = SpanContext.new(id: LightStep.guid, trace_id: ref.trace_id, sampled: ref.sampled?)
         set_baggage(ref.baggage)
         set_tag(:parent_span_guid, ref.id)
       else
@@ -83,6 +83,7 @@ def set_baggage_item(key, value)
       @context = SpanContext.new(
         id: context.id,
         trace_id: context.trace_id,
+        sampled: context.sampled?,
         baggage: context.baggage.merge({key => value})
       )
       self
@@ -94,6 +95,7 @@ def set_baggage(baggage = {})
       @context = SpanContext.new(
         id: context.id,
         trace_id: context.trace_id,
+        sampled: context.sampled?,
         baggage: baggage
       )
     end
diff --git a/lib/lightstep/span_context.rb b/lib/lightstep/span_context.rb
index cbbf986..573b45a 100644
--- a/lib/lightstep/span_context.rb
+++ b/lib/lightstep/span_context.rb
@@ -20,12 +20,12 @@ def initialize(id:, trace_id:, sampled: true, baggage: {})
 
     def truncate_id(id)
       return id unless id && id.size == 32
-      id[16..-1]
+      id[0...16]
     end
 
     def pad_id(id)
       return id unless id && id.size == 16
-      "#{ZERO_PADDING}#{id}"
+      "#{id}#{ZERO_PADDING}"
     end
   end
 end
diff --git a/spec/lightstep/propagation/b3_propagator_spec.rb b/spec/lightstep/propagation/b3_propagator_spec.rb
index be0b75d..76345d1 100644
--- a/spec/lightstep/propagation/b3_propagator_spec.rb
+++ b/spec/lightstep/propagation/b3_propagator_spec.rb
@@ -2,9 +2,9 @@
 
 describe LightStep::Propagation::B3Propagator, :rack_helpers do
   let(:propagator) { subject }
-  let(:trace_id_high_bytes) { LightStep.guid }
-  let(:trace_id_low_bytes) { LightStep.guid }
-  let(:trace_id) { [trace_id_high_bytes, trace_id_low_bytes].join }
+  let(:trace_id_msb) { LightStep.guid }
+  let(:trace_id_lsb) { LightStep.guid }
+  let(:trace_id) { [trace_id_msb, trace_id_lsb].join }
   let(:span_id) { LightStep.guid }
   let(:baggage) do
     {
@@ -19,10 +19,10 @@
       baggage: baggage
     )
   end
-  let(:span_context_trace_id_low_bytes) do
+  let(:span_context_trace_id_8_byte) do
     LightStep::SpanContext.new(
       id: span_id,
-      trace_id: trace_id_low_bytes,
+      trace_id: trace_id_lsb,
       baggage: baggage
     )
   end
@@ -76,8 +76,8 @@
     it 'pads 8 byte trace_ids' do
       carrier = {}
 
-      propagator.inject(span_context_trace_id_low_bytes, OpenTracing::FORMAT_RACK, carrier)
-      expect(carrier['x-b3-traceid']).to eq('0' * 16 << trace_id_low_bytes)
+      propagator.inject(span_context_trace_id_8_byte, OpenTracing::FORMAT_RACK, carrier)
+      expect(carrier['x-b3-traceid']).to eq(trace_id_lsb + '0' * 16)
       expect(carrier['x-b3-spanid']).to eq(span_id)
     end
   end
@@ -88,7 +88,7 @@
       propagator.inject(span_context, OpenTracing::FORMAT_TEXT_MAP, carrier)
       extracted_ctx = propagator.extract(OpenTracing::FORMAT_TEXT_MAP, carrier)
 
-      expect(extracted_ctx.trace_id).to eq(trace_id_low_bytes)
+      expect(extracted_ctx.trace_id).to eq(trace_id_msb)
       expect(extracted_ctx.trace_id16).to eq(trace_id)
       expect(extracted_ctx.id).to eq(span_id)
       expect(extracted_ctx.baggage['footwear']).to eq('cleats')
@@ -105,7 +105,7 @@
       propagator.inject(span_context, OpenTracing::FORMAT_RACK, carrier)
       extracted_ctx = propagator.extract(OpenTracing::FORMAT_RACK, to_rack_env(carrier))
 
-      expect(extracted_ctx.trace_id).to eq(trace_id_low_bytes)
+      expect(extracted_ctx.trace_id).to eq(trace_id_msb)
       expect(extracted_ctx.trace_id16).to eq(trace_id)
       expect(extracted_ctx.id).to eq(span_id)
       expect(extracted_ctx.baggage['footwear']).to eq('cleats')
@@ -135,7 +135,7 @@
       )
       expect(extracted_ctx.id).to eq(span_id)
       expect(extracted_ctx.trace_id16).to eq(trace_id)
-      expect(extracted_ctx.trace_id).to eq(trace_id_low_bytes)
+      expect(extracted_ctx.trace_id).to eq(trace_id_msb)
     end
 
     it 'handles carriers with string keys' do
@@ -148,7 +148,7 @@
 
       expect(string_ctx).not_to be_nil
       expect(string_ctx.trace_id16).to eq(trace_id)
-      expect(string_ctx.trace_id).to eq(trace_id_low_bytes)
+      expect(string_ctx.trace_id).to eq(trace_id_msb)
       expect(string_ctx).to be_sampled
       expect(string_ctx.id).to eq(span_id)
     end
@@ -163,21 +163,21 @@
 
       expect(symbol_ctx).not_to be_nil
       expect(symbol_ctx.trace_id16).to eq(trace_id)
-      expect(symbol_ctx.trace_id).to eq(trace_id_low_bytes)
+      expect(symbol_ctx.trace_id).to eq(trace_id_msb)
       expect(symbol_ctx).to be_sampled
       expect(symbol_ctx.id).to eq(span_id)
     end
 
     it 'pads 8 byte trace_ids' do
       carrier = {
-        'x-b3-traceid' => trace_id_low_bytes,
+        'x-b3-traceid' => trace_id_lsb,
         'x-b3-spanid' => span_id,
         'x-b3-sampled' => '1'
       }
 
       extracted_ctx = propagator.extract(OpenTracing::FORMAT_TEXT_MAP, carrier)
-      expect(extracted_ctx.trace_id16).to eq('0' * 16 << trace_id_low_bytes)
-      expect(extracted_ctx.trace_id).to eq(trace_id_low_bytes)
+      expect(extracted_ctx.trace_id16).to eq(trace_id_lsb + '0' * 16)
+      expect(extracted_ctx.trace_id).to eq(trace_id_lsb)
     end
 
     it 'interprets a true sampled flag properly' do
@@ -209,7 +209,7 @@
       extracted_ctx = propagator.extract(OpenTracing::FORMAT_TEXT_MAP, carrier)
       expect(extracted_ctx.trace_id16).to eq(trace_id)
       expect(extracted_ctx.trace_id16.size).to eq(32)
-      expect(extracted_ctx.trace_id).to eq(trace_id_low_bytes)
+      expect(extracted_ctx.trace_id).to eq(trace_id_msb)
       expect(extracted_ctx.trace_id.size).to eq(16)
     end
   end
diff --git a/spec/lightstep/propagation/lightstep_propagator_spec.rb b/spec/lightstep/propagation/lightstep_propagator_spec.rb
index c49e630..5af0d1a 100644
--- a/spec/lightstep/propagation/lightstep_propagator_spec.rb
+++ b/spec/lightstep/propagation/lightstep_propagator_spec.rb
@@ -3,7 +3,7 @@
 describe LightStep::Propagation::LightStepPropagator, :rack_helpers do
   let(:propagator) { subject }
   let(:trace_id) { LightStep.guid }
-  let(:padded_trace_id) { '0' * 16 << trace_id }
+  let(:padded_trace_id) { trace_id + '0' * 16 }
   let(:span_id) { LightStep.guid }
   let(:baggage) do
     {
@@ -153,7 +153,7 @@
     end
 
     it 'maintains 8 and 16 byte trace ids' do
-      trace_id16 = [LightStep.guid, trace_id].join
+      trace_id16 = [trace_id, LightStep.guid].join
 
       carrier = {
         'ot-tracer-traceid' => trace_id16,
diff --git a/spec/lightstep_spec.rb b/spec/lightstep_spec.rb
index f3f7a81..c424df8 100644
--- a/spec/lightstep_spec.rb
+++ b/spec/lightstep_spec.rb
@@ -72,6 +72,20 @@ def init_callback_tracer(callback)
     expect(child_span.span_context.baggage).to eq(parent_span.span_context.baggage)
   end
 
+  it 'should inherit true sampled flag from parent span' do
+    tracer = init_test_tracer
+    parent_ctx = LightStep::SpanContext.new(id: LightStep.guid, trace_id: LightStep.guid, sampled: true)
+    child_span = tracer.start_span('child_span', child_of: parent_ctx)
+    expect(child_span.span_context).to be_sampled
+  end
+
+  it 'should inherit false sampled flag from parent span' do
+    tracer = init_test_tracer
+    parent_ctx = LightStep::SpanContext.new(id: LightStep.guid, trace_id: LightStep.guid, sampled: false)
+    child_span = tracer.start_span('child_span', child_of: parent_ctx)
+    expect(child_span.span_context).not_to be_sampled
+  end
+
   it 'should allow operation_name updates' do
     tracer = init_test_tracer
     span = tracer.start_span('original')