This book covers all aspects of hybrid breeding technologies applied for crop improvement in major field crops. The different male sterility systems such as genetic male sterility (GMS), cytoplasmic male sterility (CMS), cytoplasmic and genetic male sterility (CGMS), and male sterility induced by the photoperiod (PGMS), temperature (TGMS), and chemicals are discussed in detail. The different chapters in this book provide a timeline of the key breakthroughs witnessed in the field of plant male sterility technologies, their application in hybrid breeding, and the relevance to the current need for food security.