This book advances an evidence-based, unifying conceptual view of sarcoidosis that accounts for many of its baffling and seemingly paradoxical features. It thoroughly explores certain aspects of sarcoidosis—including its fundamental nature, causation, relationship to neoplasia, and appropriate treatment—in which prevailing premises either lack support or are opposed by a critical analysis of available data. Where possible, the text transcends description by positing plausible pathogenetic mechanisms. The final chapter sketches 20 fundamental questions, suitable candidates for future investigation, modeled after Hilbert's justly famed 1900 address to mathematicians at the Second International Congress.