This treaty on long-term sick leave (medical pensions, disability benefits) is a much-needed book, contributing to everyday practice. It will be very useful both for physicians and patients, legislators and insurers, linguists and philosophers. It is a unique book about insurance medicine, that discusses medicine from an International Classification of Functioning, Disability, and Health point of view. Invalidity pension is a very important topic, not discussed in the medical faculty. Obtaining a disability pension is a process that implies (1) patient evaluation, (2) handing over of money (file evaluation, funds transfer), (3) patient and societal acceptance of disability and (4) rehabilitation.This treaty will tackle the difficult aspects of definitions, ethics, a comparison of medical criteria for patient evaluation, aspects of risks, evolution and prognosis. Disability assessment in the UK, USA, and EU is presented. Errors in the electrocardiograms, the lab analyses or the spirometry interpretation are detailed separately. This book also discusses the pulmonary and visual rehabilitation. The return to work, part of the rehabilitation process, is one of the Social Determinants of Health (SDH), non-medical factors that influence the health outcomes. SDH became more important after the development of Artificial Intelligence and the construction of huge databases in health.