The BMW X3 is an SUV manufactured by BMW since 2003, based on the BMW 3 Series platform. Now in its fourth generation, BMW markets the car as a Sports Activity Vehicle, the company's proprietary descriptor for its X-line luxury vehicles.

The first-generation X3 was designed by BMW in conjunction with Magna Steyr of Graz, Austria—who also manufactured all X3s under contract to BMW. BMW manufactured the second-generation X3 at their Spartanburg plant in South Carolina, United States. Starting with the third generation, BMW South Africa's Rosslyn plant began production of the X3, alongside the Spartanburg plant, after the facility underwent a major upgrade to prepare for the X3 production, replacing the long-running 3 Series production in the plant. About 76,000 units will be manufactured there annually.

The car was the first mid-size, premium SUV on the market. In 2008, BMW started competing with the Mercedes-Benz GLK-Class (renamed GLC-Class since 2016), and numerous other SUVs in this segment. The X3 is smaller than the X5 and X6, and bigger than the X1 and the X2.

An all-electric variant is sold as the BMW iX3.