An introduction to relativistic processes and the standard model of electroweak interactions These notes are designed as a guide line for a course in Elementary Particle Physics for undergraduate students. The purpose is providing a rigorous and self contained presentation of the theoretical framework and of the phenomenological aspects of the physics of interactions among fundamental constituents of matter. The first part of the volume is devoted to the description of scattering processes in the context of relativistic quantum field theory. The use of the semi classical approximation allows us to illustrate the relevant computation techniques in a reasonably small amount of space. Our approach to relativistic processes is original in many respects. The second part contains a detailed description of the construction of the standard model of electroweak interactions with special attention to the mechanism of particle mass generation. The extension of the standard model to include neutrino masses is also described. We have included a number of detailed computations of cross sections and decay rates of pedagogical and phenomenological relevance.