Health issues in the context of aging are becoming an increasing concern to individuals, health care providers, and health care systems. This is, to a large extent, a result of the increasing prominence of persons aged 50 and older who comprise the global population. Not only has the number of older persons in the world tripled over the past 50 years, but it is expected to more than triple again over the next 50 years. In fact, the older population is growing at a faster rate than the total population in almost all regions of the world! As an example of this growth, consider the following. In 1950, only three countries in the world—China, India, and the United States—had more than 10 million people aged 60 years and older. In 2000, the number of countries with more than 10 million individuals aged 60 or older increased to 12. It is anticipated that by the year 2050, 33 countries will have more than 10 million people who are 60 years of age or older; of these, 5 countries will likely have more than 50 million people who are 60 years old or older. Aging is a complex developmental process that is, as yet, poorly understood. From a physical perspective, aging involves a loss of resilience or reserve capacity to respond to stressors, and this acquired vulnerability usually means that aging is associated with some greater susceptibility to illness as well as some decline in function over time. Nevertheless, the effects of aging are highly variable; some men and women are still running races at the age of 82, while others are frail and bed‐bound in a nursing home. In this brief overview, the physiology of aging in the major organ systems, what is known about the human life span, and different theories of aging are outlined.