This book contains basic information in molecular biology and is divided into four chapters. Each chapter is much simplified to enable beginners to understand the basic concepts of molecular biology. It begins with the chromosomes as a unit in living cells that consists of DNA molecule bonded to various proteins. It then introduces nucleic acids: RNA and types, DNA replication, genetic code, eukaryotic and prokaryotic gene expression and how they regulate their expression. The book also covers extra chromosomal DNA. Therefore, it is suitable and recommended for beginners in molecular biology especially the undergraduate biological or medical science students and any other individual who is interested in understanding the basics of molecular biology.