Dog agility is a sport in which a handler is given a set amount of time in which to direct a dog off-leash through an obstacle course. Agility made its debut as an entertainment for spectators at the Crufts Dog Show in 1979; it has since become the most rapidly growing dog sport in England, Western Europe and North America. Spectators continue today to get caught up watching the dog and handler's  enthusiasm in their athletic race against the clock. 

In the United States, there are several national organizations for agility which sanction tests or trials held by local dog training clubs. Trials which are based on the original international rules and specifications call for the highest level of agility from the dogs both in terms of speed and the physical ability to perform the obstacles. There are also domestic varieties of the sport that call for less actual agility (by using lower jump heights and smaller obstacles) from the dog and focus more on the handling aspects of the game. 

There are several obstacles common to all the different organizations: 
Pipe Tunnel
Weave Poles
A-Frame
Dog Walk
See-Saw
Collapsed Tunnel
Pause Table
Tire or Hoop Jump
Various Types of Jumps

The obstacles used in agility have been designed with both safety and spectator appeal in mind. All jumps have easily displaceable bars so that the dog should not experience injury should he misjudge and take down a jump bar. All obstacles that the dog must physically scale have 'contact' zones painted on the equipment; the contact zones enforce safe training techniques since handlers know that dogs will be faulted unless one or more feet are in the contact zones when ascending or descending these contact obstacles. All contact equipment surfaces are roughened for good traction in both dry and wet weather. 

In competition, the obstacles are arranged in various course configurations, always unique from trial to trial, that offer levels of challenges appropriate to the class and experience level of the dogs competing. The handler must direct their dog around the course in the sequence that has been predetermined by the judge. At the entry levels of competitions, courses contain few complications and are more of a test to prove the dog can competently perform the equipment within a reasonable amount of time. As the dog and handler earn their way into successively higher levels, the courses increase in complexity and begin to require split second timing and coordination between the handler and dog in order to accomplish the course within the 'Standard Course Time' (SCT) established by the judge. 

The rules are fairly simple; handlers may give an unlimited number of commands or signals to their dogs, but may not touch either the equipment or the dog. Dogs are 'faulted' for actions such as taking down a jump bar, failing to put one or more feet in the safety or contact zone when ascending or descending contact equipment, taking obstacles out of sequence, and running past or stopping before the next obstacle to be performed. Time penalties are additionally assessed against dogs that exceed the SCT. 

Dogs compete only against dogs of similar height at the withers within a fixed number of jump height divisions. The number of height divisions and the ranges of dog heights assigned to a height division (and therefore the difficulty factor) differ considerably from organization to organization.  Regardless of the organization, the dog with the lowest number of faults and the fastest time wins the class or height division. 

Agility trials are a sport and all participants should be guided by the principles of good sportsmanship both in and outside the trial course.