Due to its specific bacterial-killing nature, many studies have focused on understanding the biological functions and molecular mechanisms of bacteriophages. In recent years, phage therapy re-emerges as an efficient tool in the treatment of bacterial infections, especially for multi-drug resistant bacterial pathogens, due to its advantages over chemical antibiotics. In this book, we aim to explore recent advances in the study of diversity, genomics, and clinical applications of bacteriophages with special interests in the diversity and evolution of bacteriophages, computational analysis of uncultivated phage genomes, and bacteriophage genome engineering. With the development of metagenomics, it is revealed that the gut bacterial community plays important role in humans. However, less is known about the functions of the viral microbiome in human health and diseases, which will also be a focus of the book. Finally, the development of bacteriophage therapy will be explored to facilitate the application of the approach in real-world situations.