The aim of this book is to present recent concepts in molecular biology with focus on the application to human, animal and plant pathology, in numerous aspects like diagnosis, prevention and treatment of diseases, prognosis, etiology and use of these methodologies in comprehending the pathophysiology of several diseases that impact living beings. Some of the topics covered are PCR-types; limitations and utilities; PCR in food analysis; gene expression analysis and combinatory qPCR technology. This book will broaden the knowledge in molecular biology and will be useful for students, researchers and professionals.