Complaints and disciplinary processes play a significant role in health professional regulation. Many countries are transitioning from models of self-regulation to greater external oversight through systems including meta-regulation, responsive (risk-based) regulation, and "networked governance". Such systems harness, in differing ways, public, private, professional and non-governmental bodies to exert influence over the conduct of health professionals and services. Interesting literature is emerging regarding complainants' motivations and experiences, the impact of complaints processes on health professionals, and identification of features such as complainant and health professional profiles, types of complaints and outcomes. This article concentrates on studies identifying vulnerable groups and their participation in health care regulatory systems.