A breast implant is a prosthesis used to change the size, shape, and contour of a woman's breast. In reconstructive plastic surgery, breast implants can be placed to restore a natural looking breast mound for post–mastectomy breast reconstruction patients or to correct congenital defects and deformities of the chest wall. They are also used cosmetically to enhance or enlarge the appearance of the breast through breast augmentation surgery.

There are three general types of breast implant devices, defined by their filler material: saline solution, silicone gel, and composite filler. The saline implant has an elastomer silicone shell filled with sterile saline solution during surgery; the silicone implant has an elastomer silicone shell pre-filled with viscous silicone gel; and the alternative composition implants featured miscellaneous fillers, such as soy oil, polypropylene string, etc. Composite implants are typically not recommended for use anymore and, in fact, their use is banned in the United States and Europe due to associated health risks and complications.
In surgical practice, for the reconstruction of a breast, the tissue expander device is a temporary breast prosthesis used to form and establish an implant pocket for the future permanent breast implant. For the correction of male breast defects and deformities, the pectoral implant is the breast prosthesis used for the reconstruction and the aesthetic repair of a man's chest wall (see: gynecomastia and mastopexy).