Overview of this text: it is designed for the first course in mechanics of materials - or strength of materials - offered to engineering students in the sophomore or junior year. The main objective is to help develop in the engineering student the ability to analyse a given problem in a simple and logical manner and to apply to its solution a few fundamental and well-understood principles. In this text, the study of the mechanics of materials is based on the understanding of a few basic concepts and on the use of simplified models. This approach makes it possible to develop all the necessary formulas in a rational and logical manner and to clearly indicate the conditions under which they can be safely applied to the analysis and design of actual engineering structures and machine components.