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 the computational algorithms based on these theories are described in details. The code is applied to study acceleration of electrons in the laser target interaction region, propagation of hot electron beam inside a cold dielectric target and acceleration of ions from the rear side of laser irradiated thin foils.