Bodybuilding is the practice of progressive resistance exercise to build, control, and develop one's muscles via hypertrophy. An individual who engages in this activity is referred to as a bodybuilder. It is primarily undertaken for aesthetic purposes over functional ones, distinguishing it from similar activities such as powerlifting and calisthenics.

In competitive bodybuilding, competitors appear onstage in line-ups and perform specified poses (and later individual posing routines) for a panel of judges who rank them based on conditioning, muscularity, posing, size, stage presentation, and symmetry. Bodybuilders prepare for competitions by exercising and eliminating non-essential body fat. This is enhanced at the final stage by a combination of carbohydrate loading and dehydration to achieve maximum muscle definition and vascularity. Most bodybuilders also tan and shave their bodies prior to competition.

Bodybuilding requires significant time and effort to reach the desired results. A novice bodybuilder may be able to gain 8–15 pounds (4–7 kg) of muscle per year if they lift weights for seven hours per week, but muscle gains begin to slow down after the first two years to about 5–15 pounds (2–7 kg) per year. After five years, gains can decrease to as little as 3–10 pounds (1–5 kg) per year. Some bodybuilders use anabolic steroids and other performance-enhancing drugs to build muscles and recover from injuries faster. However, using performance-enhancing drugs can have serious health risks. Furthermore, most competitions prohibit the use of these substances. Despite some calls for drug testing to be implemented, the National Physique Committee (considered the leading amateur bodybuilding federation) does not require testing.

The winner of the annual IFBB Mr. Olympia contest is recognized as the world's top male professional bodybuilder. Since 1950, the NABBA Universe Championships have been considered the top amateur bodybuilding contests, with notable winners including Ronnie Coleman, Jay Cutler, Steve Reeves, and Arnold Schwarzenegger.

Stone-lifting competitions were practiced in ancient Egypt, Greece, and Tamilakam.

Western weightlifting developed in Europe from 1880 to 1953, with strongmen displaying feats of strength for the public and challenging each other. The focus was not on their physique, and they possessed relatively large bellies and fatty limbs compared to bodybuilders of today.

Bodybuilding developed in the late 19th century, promoted in England by the German Eugen Sandow, now considered as the "Father of Modern Bodybuilding". He allowed audiences to enjoy viewing his physique in "muscle display performances". Although audiences were thrilled to see a well-developed physique, the men simply displayed their bodies as part of strength demonstrations or wrestling matches. Sandow had a stage show built around these displays through his manager, Florenz Ziegfeld. The Oscar-winning 1936 musical film The Great Ziegfeld depicts the beginning of modern bodybuilding, when Sandow began to display his body for carnivals.

Sandow was so successful at flexing and posing his physique that he later created several businesses around his fame, and was among the first to market products branded with his name. He was credited with inventing and selling the first exercise equipment for the masses: machined dumbbells, spring pulleys, and tension bands. Even his image was sold by the thousands in "cabinet cards" and other prints.