Success of 3D applications on the Web inherently depends on object behavior and interaction. Current Web3D formats often fall short in supporting behavior modeling. This paper introduces a flexible concept for declaratively modeling 3D object behaviors. Based on Extensible 3D (X3D) a node concept is suggested with object-oriented features such as inheritance, strong typing, and polymorphism. An XML-based language Behavior3DNode serves the interface definition of new nodes. Their implementation is simplified by automated code generation. A novel grammar generation mechanism collects all existing nodes in a dynamic XML Schema. Thus new behavior nodes can be used along with built-in nodes as first class scene graph elements. A rich set of predefined behaviors is proposed, among them Animation and State Machine node collections. The concepts were successfully implemented with VRML97/X3D and integrated into a 3D component approach. Categories and Subject Descriptors H.5.1 [Information Inte...