Stochastic processes involving random variables are associated with the concepts of uncertainty or chance. Significant research areas in mathematical and applied sciences are devoted to their study. The growing interest of researchers interested in this field is caused by a variety of different applications in many areas like mechanics, acoustics, economics, medicine, biology etc. Thus, understanding the needs of practitioners and simultaneously presenting the new theoretical results is the aim of the book. This book consists of 12 chapters, which describe the basic concepts and properties of random processes.