This book presents an introduction to the Finite Element Method (FEM) and is primarily aimed at students, engineers and scientists who already know structural calculation. It starts from the matrix reformulation of the direct stiffness method to understand the enormous potential of introducing the idea of the weak formulation for the approximation of strut structure problems. The correspondence of results between the initial classical formulation and that of the FEM when using linear shape functions and Hermite polynomials, makes it possible to approach its general formulation more easily as a procedure to obtain approximate solutions of differential equations in partial derivatives. It is essential now to introduce the idea of element, which allows, from the definition of a reduced number of base functions and through a simple combination process, to approximate its real behavior and, through superposition, that of the structure.