Bacterial pili play important roles as environmental sensors, in host colonization and in biofilm formation, enabling bacteria to interact with the environment, with surfaces and with other bacteria and host cells. Most bacteria, both Gram positive and Gram negative, and almost all bacterial pathogens, are piliated. This book discusses the synthesis, structure, evolution, function and role in pathogenesis of these complex structures, and their basis for vaccine development and therapeutics for Streptococcus pathogens. It is an invaluable resource for researchers and students of medical microbiology.