It is well established that in auto-immune diseases there is a chronic systemic inflammatory process that predominantly affects the joints. This has a significant negative impact on the quality of life of patients and considerable socio-economic costs. In addition, in recent years a decline in life expectancy has been observed, either due to the complications of the disease itself or as a consequence of the treatments used. The most important predictors of mortality are the presence of a rheumatoid factor, the results of the Health Assessment Questionnaire (HAQ) and extra-articular manifestations. This book examines the prognostic factors and the causes of death, using rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) as models of auto-immune diseases.