ABSTRACT
In this introductory chapter, we provide a very brief introduction to cells and point out some general characteristics and associated terminology. A cell is the basic unit of life and all living creatures are made of cells. Nothing smaller than a cell can be truly called living, e.g., viruses, which are essentially genetic material encapsulated in a protein coat, have no ability to replicate by themselves, and are therefore nonliving. The only way in which they can replicate is by hijacking the replication machinery of a living cell, and this is what usually happens in a viral infection.
