Traditional animation of characters relies on the design of an external shape, called the skin, and an internal skeleton, composed of a hierarchy of frames, which enables one to control the deformation of the skin in a consistent and predictable way. Since it is relatively efficient, this skinning technique is widely used in computer graphics production environments. However, it also has inherent limitations. Even if a large amount of research work were to solve the other known deficiencies of the technique, the fundamental issue remains that some types of deformations can never be generated by it. Examples of this are the dynamic wrinkles of skin or clothes near joints, or inertia effects of muscles and fatty tissues when sharp movements are involved. In this thesis, we propose two modeling and animation techniques which address those specific problems, and which can be used to enhance existing animation sequences. Our first contribution addresses the addition of dynamic effects which are typical for the muscles/fatty tissues layer to kinematic deformations obtained through skinning or an equivalent technique. The dynamic effects are computed using a simplification of linear elasticity theory. To this end, dynamic elements which associate damped spring vibrations with a set of per vertex weights for the mesh, perform a so called dynamic skinning. The location, frequency and amplitude of the effects can be specified in a straightforward way by the user. On top of this layer comes a thin surface which can either represent the skin or clothes. This surface of almost constant area follows muscle and fatty tissue deformations by wrinkling when it gets compressed. In order to guide this behavior the user interactively positions and orients a deformable control curve of constant length on a mesh, and speciflies its region of influence. During the animation geometric folds are generated in real-time in the regions covered by the tool, and the mesh is locally refined on the fly where and when needed.