I am very glad to present this book of Basic Concept of Recombinant DNA Technology, written according to revised syllabus of B.Sc, M.Sc(Biotechnology, Microbiology), B.Pharm, M.Pharm, M.Sc Agriculture and Veterinary in all Indian Universities. This book is also useful for the medical students. I extend my good wishes to the students and teachers of Biotechnology and Microbiology, sincerely hope that Basic Concept of Recombinant DNA Technology, will receive a warm welcome from them. I welcome comments by readers of Basic Concept of Recombinant DNA Technology, for way to improve the book and to increase its value. Such suggestions will be seriously considered in the preparation of subsequent editions. I am very grateful to Dr. Tanusri Mandal, Associate Professor and Head, Department of Biotechnology, Oriental Institute of Science and Technology, Vidyasagar University, India for useful suggestions and help made by her time to time. Finally, I would like to thanks my wife Arpita Pattanayak(De), and my sweet daughter Anindita De for continuous encouragement for completion of this book.