Adopting an admission-to-discharge patient flow perspective has the potential to improve hospital operations. Flow paths provide insight regarding patient care needs, support resource allocation and capacity planning decisions, and improve the operational performance of the hospitals. Studying patient flow through systems engineering tools and applications can help decision makers assess and improve care delivery. This chapter presents current research and techniques used to describe, measure, and model inpatient flow. We formally define patient flow from an operational standpoint and discuss why it is crucial for operational decisions. Systems engineering techniques, which describe and analyze inpatient flow, are introduced. The chapter concludes with a discussion of emerging approaches to capture patient flow.