diff --git a/pom.xml b/pom.xml
index 4ebda06d20..d8b90cf376 100644
--- a/pom.xml
+++ b/pom.xml
@@ -28,6 +28,11 @@
             <version>3.6.2</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <version>2.7.22</version>
+        </dependency>
     </dependencies>
 
     <build>
diff --git a/src/main/java/com/datadoghq/trace/impl/Tracer.java b/src/main/java/com/datadoghq/trace/impl/Tracer.java
index 401bb953ef..2734041a72 100644
--- a/src/main/java/com/datadoghq/trace/impl/Tracer.java
+++ b/src/main/java/com/datadoghq/trace/impl/Tracer.java
@@ -7,6 +7,7 @@ import io.opentracing.propagation.Format;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
+import java.util.UUID;
 
 
 public class Tracer implements io.opentracing.Tracer {
@@ -28,14 +29,15 @@ public class Tracer implements io.opentracing.Tracer {
         private final String operationName;
         private Map<String, Object> tags = new HashMap();
         private Long timestamp;
-        private Optional<SpanContext> parent;
+        private Optional<SpanContext> parent = Optional.empty();
 
         public SpanBuilder(String operationName) {
             this.operationName = operationName;
         }
 
         public io.opentracing.Tracer.SpanBuilder asChildOf(SpanContext spanContext) {
-            return null;
+            this.parent = Optional.ofNullable(spanContext);
+            return this;
         }
 
         public io.opentracing.Tracer.SpanBuilder asChildOf(Span span) {
@@ -73,36 +75,57 @@ public class Tracer implements io.opentracing.Tracer {
         public Span start() {
 
             // build the context
-            SpanContext context = buildNewSpanContext();
+            SpanContext context = buildTheSpanContext();
 
             return new com.datadoghq.trace.impl.Span(
+                    Tracer.this,
                     this.operationName,
                     this.tags,
                     Optional.ofNullable(this.timestamp),
                     context);
         }
 
-        private SpanContext buildNewSpanContext() {
+        private SpanContext buildTheSpanContext() {
 
-            Optional<Object> parentContext = Optional.ofNullable(this.parent);
-            SpanContext context = new com.datadoghq.trace.impl.SpanContext(
-
-            );
-
-
-
-            if (this.parent == null) {
-                long traceId = 123L;
+            SpanContext context = null;
 
+            long generatedId = generateNewId();
+            if (parent.isPresent()) {
+                com.datadoghq.trace.impl.SpanContext p = (com.datadoghq.trace.impl.SpanContext) parent.get();
+                context = new com.datadoghq.trace.impl.SpanContext(
+                        p.getTraceId(),
+                        generatedId,
+                        p.getSpanId(),
+                        null,
+                        null,
+                        null,
+                        false,
+                        null,
+                        null,
+                        true);
             } else {
-
+                context = new com.datadoghq.trace.impl.SpanContext(
+                        generatedId,
+                        generatedId,
+                        0L,
+                        null,
+                        null,
+                        null,
+                        false,
+                        null,
+                        null,
+                        true);
             }
 
-            return null;
+            return context;
         }
 
         public Iterable<Map.Entry<String, String>> baggageItems() {
             return null;
         }
     }
+
+    long generateNewId() {
+        return UUID.randomUUID().getMostSignificantBits();
+    }
 }
diff --git a/src/test/java/com/datadoghq/trace/impl/SpanBuilderTest.java b/src/test/java/com/datadoghq/trace/impl/SpanBuilderTest.java
index d60f5b7d4e..ff813959d6 100644
--- a/src/test/java/com/datadoghq/trace/impl/SpanBuilderTest.java
+++ b/src/test/java/com/datadoghq/trace/impl/SpanBuilderTest.java
@@ -1,16 +1,15 @@
 package com.datadoghq.trace.impl;
 
-import org.assertj.core.data.MapEntry;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 
-import java.util.Collections;
-import java.util.Date;
 import java.util.HashMap;
 import java.util.Map;
 
-import static org.assertj.core.api.Assertions.*;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 public class SpanBuilderTest {
 
@@ -70,9 +69,9 @@ public class SpanBuilderTest {
     }
 
     @Test
-    public void shouldBuilSpanTimestampInNano() {
+    public void shouldBuildSpanTimestampInMilli() {
 
-        final long expectedTimestamp = 487517802L * 1000 * 1000;
+        final long expectedTimestamp = 487517802L * 1000;
         final String expectedName = "fakeName";
 
         Span span = (Span) tracer
@@ -83,15 +82,39 @@ public class SpanBuilderTest {
         assertThat(span.getStartTime()).isEqualTo(expectedTimestamp);
 
         // auto-timestamp in nanoseconds
-        long tick = System.nanoTime();
+        long tick = System.currentTimeMillis();
         span = (Span) tracer
                 .buildSpan(expectedName)
                 .start();
 
         // between now and now + 100ms
-        assertThat(span.getStartTime()).isBetween(tick, tick * 1000 * 100);
+        assertThat(span.getStartTime()).isBetween(tick, tick + 100);
 
     }
 
 
+    @Test
+    public void shouldLinkToParentSpan() {
+
+        final long spanId = 1L;
+        final long expectedParentId = spanId;
+
+        SpanContext mockedContext = mock(SpanContext.class);
+
+        when(mockedContext.getSpanId()).thenReturn(spanId);
+
+        final String expectedName = "fakeName";
+
+        Span span = (Span) tracer
+                .buildSpan(expectedName)
+                .asChildOf(mockedContext)
+                .start();
+
+       SpanContext actualContext = (SpanContext) span.context();
+
+        assertThat(actualContext.getParentId()).isEqualTo(expectedParentId);
+
+
+    }
+
 }
\ No newline at end of file
diff --git a/src/test/java/com/datadoghq/trace/impl/TracerTest.java b/src/test/java/com/datadoghq/trace/impl/TracerTest.java
index b571ee2fca..aa5279f73f 100644
--- a/src/test/java/com/datadoghq/trace/impl/TracerTest.java
+++ b/src/test/java/com/datadoghq/trace/impl/TracerTest.java
@@ -3,17 +3,21 @@ package com.datadoghq.trace.impl;
 
 import org.junit.Test;
 
-class TracerTest {
-    @Test
-    void buildSpan() {
-    }
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class TracerTest {
+
 
     @Test
-    void inject() {
-    }
+    public void testGenerateNewId() {
 
-    @Test
-    void extract() {
+        Tracer tracer = new Tracer();
+        long id1 = tracer.generateNewId();
+        long id2 = tracer.generateNewId();
+
+        assertThat(id1).isNotNull();
+        assertThat(id1).isNotZero();
+        assertThat(id1).isNotEqualTo(id2);
     }
 
 }
\ No newline at end of file