The global landscape of health care is changing with health systems operating in increasingly complex environments. While new treatments, technologies and care models can have therapeutic potential, they can also pose new threats to safe care. Patient safety is a fundamental principle of health care and is now being recognized as a large and growing global public health challenge. Global efforts to reduce the burden of patient harm have not achieved substantial change over the past 15 years, despite pioneering work in some health care settings. Patient safety is the absence of preventable harm to a patient during the process of health care, including the reduction of risk of unnecessary harm associated with health care to an acceptable minimum. An acceptable minimum refers to the collective notions of given current knowledge, resources available and the context in which care is delivered, weighed against the risk of non-treatment or other treatment.