The present book covers wide area of molecular biology and cytogenetic biology in a form especially suitable for graduate (PG) students and undergraduate students (UG). This book will widely help to students, teachers, academicians to aid the knowledge about the course and beyond the course related to the subject matter as given in the box. In this book, we begin by describing the history of molecular biology and cytogenetic biology. Further, we turn to the nucleic acid, types and its structure, replication, transcription, translation, DNA damage and repair mechanisms. The cytogenetics describes in the chapter 6 followed by sex determination, karyotyping , chromosomal disorder, human genome project and gene library. The chapter 10 has cancer biology, in which the role of proto-oncogenes and oncogenes, its conversion, cancer treatment, drugs and therapy is discussed. Finally, the chapter 11 includes the molecular evolution. Boxed material throughout the book is provided to illustrate the topics covered in the main text, explanations of the medical relevance and in depth sections that extend the coverage beyond the content of the main text.