Embryogenesis is the biological process of fundamental importance for the growth of life. This book is a collection of views on contemporary trends in modern biology emphasizing on gametogenesis fertilization early and/or delayed embryogenesis in animals plants and other small organisms. Written by international experts this book provides an introduction as well as in-depth review on classical as well as contemporary problems that pose a challenge in understanding how living organisms - take birth grow and reproduce at levels varying from molecular and cellular levels to individual level. Important topics covered are human embryogenesis hox genes-master regulators of the animal bodyplan plant somatic embryogenesis genomic integrity of mouse embryonic stem cells etc.