The only rule that differs from non-wheelchair tennis is the one that concerns the number of bounces a ball may take before it must be played. In wheelchair tennis the ball may bounce up to two times, the second bounce may also occur outside of the field. This also holds true for service.
Wheelchair tennis got started in the mid-70s thanks to the efforts of Brad Parks who is effectively the creator of competitive wheelchair tennis. Since then, a lot of effort has been put into the promotion of the sport in order to get rid of the therapy image that still clings to the handicapped sports today. It has been a Paralympic sport since the 1988 Summer Paralympics in Seoul, but it wasn't until Barcelona 1992 that wheelchair tennis acquired the status of a full-fledged competition. The 2000 Summer Paralympics in Sydney have boosted public awareness immensely. Some of the most thrilling action of all the Paralympic Games could be seen especially in the last two rounds of the men's tournament where local hero David Hall beat Kai Schrameyer of Germany in the semifinal and went on to win the final against Texan Steve Welch.
In the ITF men's rankings of January, 2004, Hall ranks first. The strongest woman is Esther Vergeer of the Netherlands.