In this chapter, we discuss principles of dynamics that can be used to analyze dynamic problems in a way equivalent to Newton’s fundamental laws. We first consider the concept of dynamic equilibrium, in which we understand the inertia terms in Newton’s fundamental law as so-called inertia forces. Furthermore, we introduce d’Alembert’s principle, which proves to be an extension of the principle of virtual displacements already known from statics and can be used advantageously if no information about constraint forces is required for a dynamic task. This chapter concludes with the treatment of the so-called Lagrangian equations of the second kind, which can be derived from d’Alembert’s principle and which can be used to determine the equations of motion of mechanical systems based on potential and kinetic energy.