The purpose of this book is to provide information on senescent cells and why they are prevented from multiplying via cell division. It includes main sections on the nature of Go/1 transition, factors promoting the cell cycle traverse and avoiding the Go/1 arrest, and negative factors arresting the cell cycle traverse and promoting the stay in the Go/1 stage. Filled with illustrations and explanations, it collectively presents the mechanisms that control the cellular aging process. This reference is a must for anyone with special interests in the biological community, and specifically the field of gerontology.