Existing definitions and measurement approaches of quality of health care often fail to address the complexities involved in understanding quality of care. It is perceptions of quality, rather than clinical indicators of quality, that drive service utilization and are essential to increasing demand. Here we reflect on the nature of quality, how perceptions of quality influence health systems and what such perceptions indicate about measurement of quality within health systems. We discuss six specific challenges related to the conceptualization and measurement of the quality of care: perceived quality as a driver of service utilization; quality as a concept shaped over time through experience; responsiveness as a key attribute of quality; the role of management and other so-called upstream factors; quality as a social construct co-produced by families, individuals, networks and providers; and the implications of our observations for measurement. Within the communities and societies where care is provided, quality of care cannot be understood outside social norms, relationships, trust and values. We need to improve not only technical quality but also acceptability, responsiveness and levels of patient-provider trust. Measurement approaches need to be reconsidered. An improved understanding of all the attributes of quality in health systems and their interrelationships could support the expansion of access to essential health interventions.