Clay (red European or green American [Har-Tru]) is best for baseliners because the surface is slow and it's harder to hit power shots by the baseliners. Hardcourts (outdoor or indoor (e.g. DecoTurf, Rebound Ace) are best for servers because the courts are fast and that makes your serve more effective. Lawn or grass courts are good for volleyers because the ball tends to skid and stay low, which makes the volleys hard to return. Servers also like grass for the same reason. The four Grand Slam tournaments are the Australian Open (January, Rebound Ace), The French Open (May-June, red clay), Wimbledon (June-July, grass), and the US Open (August-September, DecoTurf). There are always "tune-up" tournaments right before the Slams that are played on the same surface as the Slam. Typically, western Europeans (Spain, France) and South Americans (Argentina, Chile) tend to be clay court specialists, since these types of courts are common in those countries. Americans and Australians tend to favor hardcourts and grass. A slow patient baseline game on clay is very different from the speedy serve-and-volley game on hardcourts. Many great players have won the Australian, Wimbledon, and the US Open, yet failed again and again (often losing in the first or second round) in the French. Pete Sampras is the prime example: Australian Open: Winner ('94, '97) French Open: SemiFinalist (1996) Wimbledon: Winner ('93-'95; '97-'00) US Open: Winner ('90, '93, '95, '96, '02) Players that have won all four Slams include: Rod Laver & Steffi Graf (all 4 in same year) Martina Navratilova & Serena Williams (4 consecutive, different years) Billie Jean King, Chris Evert, Andre Agassi (various years) Here's a link to more information on this topic: http://news.bbc.co.uk/sportacademy/hi/sa/tennis/features/newsid_2209000/2209710.stm

Hard court is for those who like higher bounces and a medium speed. Clay is for those who like a medium bounce and a slow speed. Grass is for those who like fast speed and low bounce. Rafael Nadal is very good on clay courts because he is slow in his motions, and the clay allows him to catch up. He isn't bad at hard courts, but he is not very good with grass because it's much faster.