Prediction and assessment of seated postures are essential for ergonomic vehicle design whereas dynamic seat interactions are essential for impact conditions. This paper presents seat models and human models for both applications. An interface has been developed to convert RAMSIS human models and postures to MADYMO. Static seat interaction analyses with RAMSIS provide estimated postures and a qualitative comfort assessment. MADYMO simulations allow analysis of required muscular joint torques as well as seat contact forces and pressures. An example is included where a realistic posture is derived to simulate rearward impact loading.