The purpose of the present study was, by means of a literature review, to describe and analyse the characteristics of clinical indicators used to assess and promote quality improvement in nursing care. It was found that a generally accepted definition of a clinical indicator is a 'quantitative measure that can be used as a guide to monitor and evaluate the quality of important patient care and support service activities'. By the seriousness of the event and the degree to which it can be avoided, clinical indicators are described as sentinel event or rate-based indicators. They can measure structure, process or outcome of care. Authors have had different approaches in focus when selecting and developing indicators viz. specific aspects of care/nursing diagnosis, medical diagnosis, generic aspects of care and clinical areas. These different points of departure were influenced by research knowledge, theories/frameworks, or by the opinions of patients or staff. The threshold of an indicator is essential when measuring the quality of care as it describes a critical level between what is considered good or not. Thresholds should be dynamic, realistic, and improve over time. However, the literature on how to establish specific thresholds is limited. The review has also revealed that there is an uncertainty regarding the use of terms such as indicators, standards, norm, criteria and aspects of care.