Medication safety is central to patient outcomes and system costs. This chapter summarizes the scale of medication errors, their harms, and economic burden, then maps where failures occur across the medicines pathway: selection and formulary, procurement, storage, indenting and inventory, prescribing (including verbal orders), transcription, prescription, dispensing, preparation, and administration and communication and outline methods to prevent these errors. Prevention and reporting of adverse drug reactions (ADRs), pharmacovigilance, event reporting, and harm categorization are covered to support learning and feedback. A systems approach, human factors, reliable processes, and a just culture anchors practical steps to cut preventable harm and cost.