Quality in healthcare is not directly observable and measurable. Quality indicators serve as a tool for operationalizing quality of care. Different quality measures are required depending on the purpose, context, and audience concerned. The methodological quality of the indicators themselves has to be critically assessed. Various quality requirements for indicators have been published and can be described based on the steps of the developmental process. Importance, scientific acceptability, usability, and feasibility are reported as basic criteria for assessment. The QUALIFY instrument offers a standardized approach for assessing quality indicators and reflects best current practice. Measuring quality through indicators is no end in itself. The effect of measurement on motivating quality improvement must be evaluated in future studies.