diff --git a/src/main/java/pythagoras/f/AbstractCircle.java b/src/main/java/pythagoras/f/AbstractCircle.java
new file mode 100644
index 0000000..71e507c
--- /dev/null
+++ b/src/main/java/pythagoras/f/AbstractCircle.java
@@ -0,0 +1,62 @@
+//
+// Pythagoras - a collection of geometry classes
+// http://github.com/samskivert/pythagoras
+
+package pythagoras.f;
+
+import pythagoras.util.Platform;
+
+/**
+ * Provides most of the implementation of {@link ICircle}, obtaining only the location and radius
+ * from the derived class.
+ */
+public abstract class AbstractCircle implements ICircle
+{
+    @Override // from ICircle
+    public boolean intersects (ICircle c) {
+        return Points.distanceSq(x(), y(), c.x(), c.y()) < (radius() + c.radius());
+    }
+
+    @Override // from ICircle
+    public boolean contains (IPoint p) {
+        return Points.distanceSq(x(), y(), p.x(), p.y()) < radius();
+    }
+
+    @Override // from ICircle
+    public boolean contains (float x, float y) {
+        return Points.distanceSq(x(), y(), x, y) < radius();
+    }
+
+    @Override // from ICircle
+    public Circle offset (float x, float y) {
+        return new Circle(x() + x, y() + y, radius());
+    }
+
+    @Override // from ICircle
+    public Circle offset (float x, float y, Circle result) {
+        result.set(x() + x, y() + y, radius());
+        return result;
+    }
+
+    @Override // from ICircle
+    public Circle clone () {
+        return new Circle(this);
+    }
+
+    @Override
+    public boolean equals (Object obj) {
+        if (obj == this) {
+            return true;
+        }
+        if (obj instanceof AbstractCircle) {
+            AbstractCircle c = (AbstractCircle)obj;
+            return x() == c.x() && y() == c.y() && radius() == c.radius();
+        }
+        return false;
+    }
+
+    @Override
+    public int hashCode () {
+        return Platform.hashCode(x()) ^ Platform.hashCode(y()) ^ Platform.hashCode(radius());
+    }
+}
diff --git a/src/main/java/pythagoras/f/Circle.java b/src/main/java/pythagoras/f/Circle.java
new file mode 100644
index 0000000..1c2e39d
--- /dev/null
+++ b/src/main/java/pythagoras/f/Circle.java
@@ -0,0 +1,79 @@
+//
+// Pythagoras - a collection of geometry classes
+// http://github.com/samskivert/pythagoras
+
+package pythagoras.f;
+
+import java.io.Serializable;
+
+/**
+ * Represents a circle on a plane.
+ */
+public class Circle extends AbstractCircle implements Serializable
+{
+    /** The x-coordinate of the circle. */
+    public float x;
+
+    /** The y-coordinate of the circle. */
+    public float y;
+
+    /** The radius of the circle. */
+    public float radius;
+
+    /**
+     * Constructs a circle at (0, 0) with radius 0
+     */
+    public Circle () {
+    }
+
+    /**
+     * Constructs a circle with the specified properties
+     */
+    public Circle (float x, float y, float radius) {
+        set(x, y, radius);
+    }
+
+    /**
+     * Constructs a circle with the specified properties
+     */
+    public Circle (IPoint p, float radius) {
+        this(p.x(), p.y(), radius);
+    }
+
+    /**
+     * Constructs a circle with properties equal to the supplied circle.
+     */
+    public Circle (ICircle c) {
+        this(c.x(), c.y(), c.radius());
+    }
+
+    /** Sets the properties of this circle to be equal to those of the supplied circle.
+     * @return a reference to this this, for chaining. */
+    public Circle set (ICircle c) {
+        return set(c.x(), c.y(), c.radius());
+    }
+
+    /** Sets the properties of this circle to the supplied values.
+     * @return a reference to this this, for chaining. */
+    public Circle set (float x, float y, float radius) {
+        this.x = x;
+        this.y = y;
+        this.radius = radius;
+        return this;
+    }
+
+    @Override
+    public float x () {
+        return x;
+    }
+
+    @Override
+    public float y () {
+        return y;
+    }
+
+    @Override
+    public float radius () {
+        return radius;
+    }
+}
diff --git a/src/main/java/pythagoras/f/ICircle.java b/src/main/java/pythagoras/f/ICircle.java
new file mode 100644
index 0000000..a1a9b92
--- /dev/null
+++ b/src/main/java/pythagoras/f/ICircle.java
@@ -0,0 +1,42 @@
+//
+// Pythagoras - a collection of geometry classes
+// http://github.com/samskivert/pythagoras
+
+package pythagoras.f;
+
+/**
+ * Provides read-only access to a {@link Circle}.
+ */
+public interface ICircle
+{
+    /** Returns this circle's x-coordinate. */
+    float x ();
+
+    /** Returns this circle's y-coordinate. */
+    float y ();
+
+    /** Returns this circle's radius. */
+    float radius ();
+
+    /** Returns true if this circle intersects the supplied circle. */
+    boolean intersects (ICircle c);
+
+    /** Returns true if this circle contains the supplied point. */
+    boolean contains (IPoint p);
+
+    /** Returns true if this circle contains the specified point. */
+    boolean contains (float x, float y);
+
+    /** Translates the circle by the specified offset.
+     * @return a new Circle containing the result.
+     */
+    Circle offset (float x, float y);
+
+    /** Translates the circle by the specified offset and stores the result in the supplied object.
+     * @return a reference to the result, for chaining.
+     */
+    Circle offset (float x, float y, Circle result);
+
+    /** Returns a mutable copy of this circle. */
+    Circle clone ();
+}