Hypertension is the most powerful, independent, preventable risk factor for death and disability from cardiovascular diseases. It is also a leading risk factor for all-cause mortality and the largest contributor to global disability-adjusted life years (DALYs). In 2015, exposure to high systolic blood pressure (BP) accounted for 10.7 million deaths (33.2% of deaths attributed to all risk factors) and nearly 212 million DALYs or 20.9% of DALYs from all risk factors. Epidemiological research over the past half-century has confirmed that the risk from hypertension is strong, continuous, graded, and doubles for each increment of 20 mmHg systolic blood pressure (BP) or 10 mmHg diastolic BP in adults, without evidence of a threshold down to BPs as low as 115/75 mmHg. In children and adolescents, hypertension prevalence is increasing (in concert with the continuing epidemic of obesity) and raised BP in adolescents remains the strongest predictor of hypertension in adults. Over the last 25 years, the global age-standardized summary exposure to hypertension has increased for men but not for women. A pooled analysis of 1479 population-based measurements covering more than 19 million participants over four decades showed that the number of adults with hypertension increased from 594 million in 1975 to 1.13 billion in 2015. Most of the increase occurred in low- and middle-income countries. Globally, the highest BP levels have shifted from high-income countries to low-income countries in south Asia and sub-Saharan Africa while BP levels have remained persistently high in central and eastern Europe.