Precisely defining the different applications of patient-reported outcome measures (PROs) in clinical practice can be difficult. This is because the intervention is complex and varies amongst different studies in terms of the type of PRO used, how the PRO is fed back, and to whom it is fed back. A theory-driven approach is used to describe six different applications of PROs in clinical practice. The evidence for the impact of these applications on the process and outcomes of care are summarised. Possible explanations for the limited impact of PROs on patient management are then discussed and directions for future research are highlighted. The applications of PROs in clinical practice include screening tools, monitoring tools, as a method of promoting patient-centred care, as a decision aid, as a method of facilitating communication amongst multidisciplinary teams (MDTs), and as a means of monitoring the quality of patient care. Evidence from randomised controlled trials suggests that the use of PROs in clinical practice is valuable in improving the discussion and detection of HRQoL problems but has less of an impact on how clinicians manage patient problems or on subsequent patient outcomes. Many of the reasons for this may lie in the ways in which PROs fit (or do not fit) into the routine ways in which patients and clinicians communicate with each other, how clinicians make decisions, and how healthcare as a whole is organised. Future research needs to identify ways in with PROs can be better incorporated into the routine care of patients by combining qualitative and quantitative methods and adopting appropriate trial designs.