Clay tennis courts are made of different combinations of crushed stones, gravel, and bricks. Most popular in Europe and South America, clay courts tend to be cheaper to make, but more costly to upkeep than more common hard surface courts.
In general, clay courts are said to play "slower" than grass or hard courts, because the clay encourages higher bounce, reducing the ball's speed.
Due to the slower ball speed that is seen on clay courts, these courts favor defensive players, who rely less on overpowering their opponent with intense serves and instead are more technically advanced and have better stamina. The slow ball speed results in longer points, less "winners" (excellent shots that are unreturnable), and softer shots with greater topspin.
There are two main versions of clay courts: red courts and green courts. Red courts are made using finely crushed shale and red brick, giving them their distinct color. Green courts, on the other hand, are made with shale and ground metabasalt, a rock with a signature black-and-white speckled appearance. When crushed, it gives courts a green-grey color. Green clay is most common in the United States. Green courts tend to play a little harder and faster than red clay courts.
Clay was initially used to protect grass courts in England during the 1800s, which could dry up or burn in the summer months. William Renshaw, one of the early tennis greats, famously kept his private courts hydrated by crushing up old clay pots that were rejected from a nearby producer.
Starting in the mid-1900s, clay courts became more popular as tennis clubs began using them with greater frequency. The company Har-Tru, one of the first leaders in the clay court business, was founded in 1931 and used stone mined from Pennsylvania for its green clay surfaces. The advent of companies that specialized in clay (like Har-Tru) expanded the popularity of clay courts even further, and today several big tournaments are played on clay courts. The Stade Roland-Garros, home to the French Open, is perhaps the most famous clay court. It utilizes a red clay surface.