Essential for the defense against all kinds of stress, small stress proteins also play major roles in the physiology, development and differentiation of human cells. In spite of their beneficial roles, small stress proteins can also be deleterious for the organism, notably in some cancer pathologies where they can, through their anti-apoptotic properties, favor tumor development and interfere with the cytotoxic activity of anti-cancer drugs. This book proposes a focus on the recent knowledge in the field of the expression and putative role of small stress proteins in human health and diseases.