Recognized principles of quality management include a component for process improvement, comprised largely of corrective and preventive action taken in response to identified problems. The importance of identifying and investigating problems has been clearly established in transfusion medicine. Such problems can be identified in the following ways: error, incident, and accident reports; adverse reaction reports; customer complaints; process indicator measurements; results of proficiency testing; and results of internal or external audits, inspections, or assessments. Responses to reported events can be remedial, in which the symptom is addressed, or corrective, in which the underlying cause is addressed with the intent to prevent recurrence. If identified problems or their root causes are trended to look for patterns or problems not yet occurring are anticipated, the action taken is proactive and considered preventive. Methods to trend events, monitor processes, and perform root cause analysis are discussed as well as use of the following process improvement 'tools': control charts, flowcharting, the 'repetitive why', cause-and-effect diagram, and Pareto analysis.