The study of retroviruses is known as retrovirology. Retroviruses are those types of RNA viruses, which insert a copy of their genome into the DNA of the cells of the organism that they invade. Such insertion changes the genome of the host cell. Those viruses are generally classified as single-stranded positive-sense RNA viruses. Once they enter the cytoplasm of the host cell, the viruses use their own reverse transcriptase enzyme to produce DNA from their RNA genomes. The virions of a retrovirus constitute of enveloped particles, which are 100 nm in diameter. The main virion components include envelope, RNA and proteins. The study of retrovirus has applications in clinical gene therapy for the long-term correction of genetic defects, such as in stem and progenitor cells. Gammaretroviral and lentiviral vectors are used for gene therapy as they mediate stable genetic modification of treated cells. These have been used in many clinical trials as treatment options for various diseases. This book is a compilation of chapters that discuss the most vital concepts and emerging trends in the field of retrovirology. The various studies that are constantly contributing towards evolution of this discipline are examined in detail. This book includes contributions of experts and scientists, which will provide innovative insights into this field.