According to Lesley Adkins and Roy A. Adkins in their Handbook to Life in Ancient Rome (1998):
Chariot racing was the oldest and most popular entertainment in the Roman world, dating back to at least the monarchy and in legend to the founding of Rome itself .... Chariot racing was very expensive and was run for profit as a highly organized business. There were four racing factions in Rome, the blues, greens, whites and reds, which were the colors worn by the charioteers. Successful charioteers became rich and famous, and portrayals of them in sculpture, mosaic, and molded glassware have survived, sometimes with their names. There was great rivalry among the factions, sometimes leading to violence among their supporters, but the greens and blues were usually the favorites.
Barbara McManus provides a thorough account of chariot racing from its origins among the Etruscans to a description of a day at the races in the Circus Maximus. Included at her site is additional information about the chariots, charioteers, and racing factions. Go Big Blue!

William Smith's Dictionary of Greek and Roman Antiqities furnishes a detailed description of the structure and features of a typical circus. It is illustrated with various diagrams and photographs and provides links to other resources. Another pertinent entry describes various types of Greek and Roman chariots.

You can watch a simulation of a chariot race and place a wager if you like!

You can take a tour of the Circus Maximus, Rome's oldest and largest venue for chariot racing.

You can test your knowledge about the Circus Maximus at the Ludi Seniles if you like!