The BMW X5 is a luxury crossover SUV introduced in 1999 as the first generation E53. It was BMW's first SUV (Sport Utility Vehicle) also known as "Four-by-Four" (4x4) in the UK. It features all-wheel drive which is branded as the "X" drive system and is available with either manual or automatic transmission.
BMW describes the X5 as a Sport Activity Vehicle (SAV) rather than an SUV, to emphasize its on-road ability despite its size. Like the Lexus RX 300 and Mercedes M-Class, the X5 heralded the shift from light truck-based body-on-frame SUVs to crossovers underpinned by unibody car platforms that would come to fruition in the late 2000s.
The E53 was developed at a time when BMW owned Land Rover and benefitted from Land Rover technology. It shared components with the Land Rover Range Rover HSE model; specifically the Hill Descent System and Off Road Engine Management system and also the BMW E39 5-series; specifically the engine and electronic system. The entire in car entertainment system (Radio Function, Navigation System, Television and Telecommunications systems, and a very flexible automotive computer system) are identical. As a result the earlier X5 models can be upgraded with newer BMW technologies (e.g. Bluetooth phone connectivity).
Source: Wikipedia, 2012