Making medical care decisions is a complex process that involves trade-offs between treatment risks and benefits and is often performed under uncertainty. Decision analysis provides the tools and theories to model these decisions analytically, aiding the development of decision support systems in healthcare settings. Health informatics professionals have an important role in implementing such systems to support medical decisions at the point of care, ensuring seamless integration without disrupting clinical workflows. Their understanding of the decision-making process and underlying theories contributes to deploying systems that can potentially improve the quality of care, patient outcomes, patient safety, and overall efficiency of care delivery. This chapter introduces the field of medical decision science and decision analysis, offering examples of common medical decision paradigms.