Plasma Immersion Ion Implantation (PIII) is a burgeoning technology in the field of surface modification as well as in semiconductor electronics. Modelling of this technique is an important aspect especially in VLSI/ULSI technology. In this work, more generalized and better realistic dynamic sheath analytical models for collisionless and collisional PIII process, incorporating sheath dynamics and its transient evaluation for multiple species plasma, have been suggested that can help in monitoring the doping and in studying the behaviour of a PIII system. The basics about PIII process technique, its applications and analytical models developed by various researchers have first been reviewed and then the analytical models suggested by the author have been discussed. To demonstrate the validity of these models, calculations for pure He, pure Ar and mixed plasma of He and Ar ions, have also been discussed in this work. This book is useful both as a graduate text as well as a research monograph for upcoming scientists, especially those who are interested in exploring the theoretical aspect of PIII technique at an analytical level.