The rotations play an extremely decisive role in the description of the Euclidean motions. The way of their representation defines the set of the problems which may be solved and the computational efficiency of the procedures. The present book is based on our research activities concerning the problems of modelling and control of rigid body motions and various applications to multibody mechanical systems. Starting with the algebraic aspects of the rigid-body motions, we involve quite naturally the vector-representation of the rotations. The kinematics and dynamics of a rigid body and multibody systems with rigid and flexible joints as well the dynamics of rigid spacecrafts are considered in the vector - parameter language. Nice mechanical applications are also treated. The book presents last tendencies in the developing of kinematics and dynamics of rigid-body chains, spacecraft stability and control, celestial mechanics, etc., and in this way may serve as a tool for students, scientists and engineers from academia and industry experienced in these attractive areas.