The importance of yeast pathogens causing life-threatening systemic and tenacious superficial infections in humans has been steadily increasing over the last few decades. Species of the genus Candida, as well as dimorphic fungi with a pathogenic yeast phase such as Histoplasma and Cryptococcus species cause systemic mycosis mainly in immunocompromised patients and following long-term therapy with broad-spectrum antibiotics and/or antifungals. In recent years, our knowledge of the molecular biology of yeast pathogens has increased dramatically and is beginning to affect diagnostic and therapeutic strategies. A wealth of new information has appeared on the key virulence factors of yeast pathogens, including dimorphism, which is one of the striking features of most yeast pathogens. Written by international experts in the field, this book introduces yeast pathogens with a comprehensive guideline on yeast systematics and taxonomy.