The number of species that comprise the family of Bartonellaceae, genus Bartonella, has recently increased from one to 11 species, five of which have been associated with different diseases and syndromes in humans. The rapidly growing number of human pathogens has led several investigators to regard bartonellosis and other associated syndromes as important emerging infectious diseases. This article presents the history and epidemiology, clinical features, diagnosis, and treatment of bartonellosis and associated diseases, including Carrion's disease, trench fever, endocarditis and bacteremia, bacillary angiomatosis, and cat-scratch disease.