Patient safety in ambulatory care settings has received less attention than in the hospital setting, where the patient safety movement originated. This systematic review commissioned by the World Health Organization examined patient safety incidents in primary care. Estimates diverged widely between studies, and most patient safety incidents did not lead to harm. However, the types of incidents most likely to cause harm were missed and delayed diagnoses and medication prescribing problems. The accompanying editorial highlights the need to implement consistent and clear definitions for patient safety incidents and associated harm and advocates for investment in research and improvement efforts for patient safety in primary care.