An exercise ball is a ball constructed of soft elastic, typically in 5 diameters of 10 cm increments, from 35 to 95 cm (14 to 37 in), and filled with air. The air pressure is changed by removing a valve stem and either filling with air or letting the ball deflate. It is most often used in physical therapy, athletic training and exercise. It can also be used for weight training.

The ball is also known by various other names, for instance: balance ball, birth ball, sitball, body ball, fitness ball, gym ball, gymnastic ball, physio ball, pilates ball, Pezzi ball, stability ball, Swedish ball, Swiss ball, therapy ball, yoga ball, or medicine ball.

The physical object known as a "Swiss Ball" was developed in 1963 by Aquilino Cosani, an Italian plastics manufacturer. He developed a process for moulding large puncture-resistant plastic balls. According to American physical therapist Joanne Posner-Mayer, the use of the exercise ball as a therapy tool probably begins with the Swiss pediatrician Dr. Elsbeth Köngan, an early advocate of the Bobath concept. Those balls, then known as "Pezzi balls", were first used in treatment programs for newborns and infants by Mary Quinton, a British physiotherapist working in Switzerland.

Later, Dr. Susanne Klein-Vogelbach, the director at the Physical Therapy School in Basel, Switzerland, integrated the use of ball exercise as physical therapy for neuro-developmental treatment. In 1985, she published a famous book “Ballgymnastik zur funktionellen Bewegungslehre” (“Ball Gymnastics for functional movement theory”), where she described several exercises with the ball. Klein-Vogelbach advocated the use of ball techniques to treat adults with orthopedic or medical problems.

In 1995, Joanne Posner-Mayer published a book "Swiss Ball Applications for Orthopedic and Sports Medicine" in the US. As American physical therapists began to use ball exercises, the term became common in the US. From their development as physical therapy in a clinical setting, those exercises are now used in athletic training, as part of a general fitness routine and incorporation in alternative exercises such as yoga and Pilates.

The fastest time to jump across 10 Swiss balls is 7.8 seconds and was achieved by Neil Whyte (Australia) on the set of CCTV - Guinness World Records Special in Beijing, China on 12 January 2016. The most push-ups performed on four Swiss balls in one minute is 31 and was achieved by Neil Whyte (Australia) on the set of CCTV Guinness World Records Special in Beijing, China, on 17 August 2011. Neil also made the record for the furthest jump between two Swiss balls at a distance of 2.3 meters in 2006.

A primary benefit of exercising with an exercise ball as opposed to exercising directly on a hard flat surface is that the body responds to the instability of the ball to remain balanced, engaging many more muscles (so-called “unstable training”). Those muscles become stronger over time to keep balance. Some dumbbell exercises, such as dumbbell fly can be performed on a ball. Ball exercises are popular among runners.

Most frequently, the core body muscles (the abdominal muscles and back muscles) are the focus of exercise ball fitness programs.