The intersection of informetrics and information retrieval (IR) research provides valuable insights for IR system modeling, design, and evaluation. This work introduces readers to informetric aspects of IR system contents and their use, and how knowledge of these patterns may be applied to better understandIR processes and their users.The recent wider availability of information retrieval technologies, due in large part to the growth of the Internet, has prompted an increase in research interest into the effective design and use of IR (information retrieval) systems. This work introduces readers to concepts of informetrics as they relate to IR, and how the intersection of these two subject areas can provide valuable insights for IR research.Informetrics, briefly summarized as the quantitative study of recorded discourse, can provide perspectives on patterns of information production and use. It also offers methodologies that may be applied in IR research that are often overlooked. Informetric analysis of IR systems can shed light on underlying patterns of IR system contents and how users interact with these systems. Applications of informetrics for IR research include the modeling and simulation of IR systems, file design and space planning, system design and implementation, system evaluation, and the targeting of services to users. Readers will learn about the scope of informetrics, informetric modeling techniques, informetric characteristics of IR systems and how they are used, and how knowledge of these characteristics may be applied in IR research.