The book presents a history of classical mechanics by focusing on issues of equilibrium, documenting the way it was studied from the fourth century BC, in Greece, until the end of the nineteenth century AD, in Europe. The adopted historical point of view restricts attention to cases where the effectiveness of forces is assessed on the basis of the virtual motion of their points of application. For completeness, hints of the alternative approach are also referred, the Archimedean for ancient mechanics and the Newtonian for modern mechanics. The laws resulting from consideration of the virtual motions are named laws of virtual work. The modern formulations of the principle of virtual work are only a particular form of them.