The BMW X3 is a compact crossover SUV marketed by the German automaker BMW since 2003. Based on the BMW 3 Series platform, and now in its second generation, BMW designed the X3 in conjunction with Magna Steyr of Graz, Austria—who manufactured all X3s under contract to BMW for the first generation. Production of the second generation vehicle has transferred to BMW's Spartanburg plant in South Carolina, United States.

Following the X5, the X3 was the second vehicle marketed by BMW as a Sports Activity Vehicle (SAV).

BMW presented the precursor to the X3 as a concept vehicle unveiled at the Detroit Auto Show in 2003. Dubbed the xActivity, BMW previewed a SAV based on the 3 Series platform, without windows and a vestigial roof.

As BMW used parts from the E39 5 Series in making the X5, likewise BMW engineers employed 3 Series parts with the X3, for example, the rear suspension from the E46 330xi.

When the BMW X3 premiered in late 2003, BMW announced that it would employ a new four-wheel drive system to power it and the X5, a system marketed as xDrive that would intervene transparently to the driver before the driver was aware of instability.