This book presents evidence that infection is cyclical with the seasons, and that this phenomenon is mirrored in cycles of immune function. The book identifies the mechanisms by which immune systems are bolstered to counteract seasonally-recurrent stressors, such as extreme temperature reductions and food shortages. Stress, infectious diseases, autoimmune diseases, and human cancers are examined, and the role of hormones such as melatonin and glucocorticoids...