This book comprises of eight chapters. Each and every chapter has been described in depth which we could have afforded, so as to benefit the student as much as possible. Every topic has been explained in the lucid language. This book is actually a sequel to our previous book "Concepts in Biotechnology". Walking on the same path we have really tried hard to make the text up to date and competitive and at the same time easy in language so as to not be difficult to learn.