We introduce 3D warp brush, a new method for interactive shape modeling in an immersive virtual reality environment. 3D warp brushes are implicitly defined tools that operate on triangle meshes. We combine the efficiency of explicit mesh representations with intuitive implicit modeling operators. The area of influence of a 3D warp brush can be of arbitrary shape since it has an associated distance field. We define different warp functions including drag, explode, and whittle. A unique feature of our framework is the ability to convert meshes into 3D warp brushes at run time. Thus, we can easily expand our set of brushes based on a small set of base brushes, such as spheres or ellipsoids. Our underlying split-edge mesh data structure supports adaptive refinement and efficient rendering with on-the-fly triangle strip generation. 3D warp brushes only operate on mesh vertices, hence, underlying mesh processing is transparent to the modeling operations. The use of a Responsive Workbench and two-handed interaction allows the user to exploit the full potential of the modeling system by intuitive and easy modification of a base surface into a desired shape. We present several models, which have been created and modified using 3D warp brushes, to demonstrate the usefulness of our framework.