Theoretical Particle Physics is traditionally one of the main research and teaching activity at SISSA since its birth. Its aim is to study and develop theories and models devoted to the understanding and unification of the four fundamental interactions in Nature. The main research lines, at present, are: Physics within and beyond the Standard Model, Astroparticle physics, String and brane theories, Quantum field theory of gravity. A Ph.D. program is entirely dedicated to the training on this field. The curriculum consists of 3-4 years of study and research. Researchers, postdocs and students can also take advantage of the rich environment of scientific institutions present in the Trieste area, such as the International Center for Theoretical Physics (ICTP), the Physics Department of the University of Trieste and the Istituto Nazionale di Fisica Nucleare (INFN).