The aim of this chapter is to provide theory on child sexual abuse (CSA). The different definitions of CSA and a formulation of an operational definition used for the purpose of this book are addressed. Types of CSA, the effects on the victim of sexual abuse and consequences on adult functioning are discussed. The information provided should be sufficient in providing a basis for understanding CSA. Additional information on different aspects related to CSA could be obtained from the list of numerous references provided. Explication of terms relevant to the concise understanding of this book is included in the final section of Chapter 1.