This chapter discusses the different types of scoring systems that include specific, generic, anatomical and functional scoring systems. The measurement of outcome is important as considerable resources are expended in providing intensive care. Outcome in intensive care can be measured with respect to mortality, morbidity, disability and quality of life. There are many influences on outcome which can be broadly grouped into patient factors, disease factors and intensive care factors. The process by which a scoring system becomes an outcome probability model is through multiple logistic regression. The scoring systems in common use in critical care include the Acute Physiology and Chronic Health Evaluation (APACHE), Simplified Acute Physiology Score (SAPS), Mortality Probability Model (MPM), Sequential Organ Failure Assessment (SOFA), Trauma and Injury Severity Score (TRISS), and the ASCOT. These scores can also be used on trauma patients in all settings.