The book is based on a theoretical study of short-pulse laser interactions with solid targets and related phenomena. Relativistic electromagnetic code based on the Particle-in-Cell method is utilized to describe laser interaction with target and subsequent transport of fast charged particles in plasma. The code is one-dimensional in space and three-dimensional in velocity and it is improved here by incorporating ionization physics and revision of binary collisional algorithm. The theories of collisional ionization, electric field ionization and elastic collisions in plasma are reviewed and...