The emergency department (ED) is an interesting field for operations research (OR) and operations management (OM) researchers. Having timevarying arrivals and heterogeneous patients that need to be treated in consecutive processing steps by several doctors, nurses and other employees, it is a complex environment to control. The difficulty to control EDs often results in (over)crowded EDs. In general, an ED is said to be experiencing periods of crowding when the demand for ED services exceeds the available ED resources (Higginson, 2012). ED crowding is a worldwide phenomenon with regional influences (Jayaprakash et al., 2009) and may cause a myriad of operational problems like patients being treated in hallways, excessive length of stay (LOS) and wait times, patients leaving without treatment or even medical errors and increased mortality. Descriptive studies that define crowding (Hwang & Concato, 2004), examine the causes and effects (Richardson & Mountain, 2009; Hoot & Aronsky, 2008; Asplin et al., 2003), and propose models to measure crowding (Hwang et al., 2011; Higginson, 2012) can be found in the medical literature. Applying OR and OM techniques to improve the performance of EDs is needed now more than ever since health budgets are tight, demand for health care services is rising and higher performance standards are being demanded simultaneously.The scope of the articles that have been selected for discussion and the search method are delineated in Section 1.1 and Section 1.2 respectively. Section 2 will provide an overview of the selected articles that use OR and OM techniques to improve ED processes. Considering the existing literature, Section 3 will outline my future research perspectives.