Dog agility is a sport in which a handler directs a dog through an obstacle course in a race for both time and accuracy. Dogs generally run off-leash with no food or toys as incentives. The handler cannot touch their dog or the obstacles, except accidentally. Consequently, the handler's can only communicate with their dog using their voice, movement, and various body signals, requiring exceptional training of both the handler and the dog.

In its simplest form, an agility course consists of a set of standard obstacles, laid out by an agility judge in a design of his own choosing on a roughly 100 by 100 foot (30 by 30 m) area, with numbers indicating the order in which the dog must complete the obstacles.

Courses are complicated enough that a dog could not complete them correctly without human direction. In competition, the handler must assess the course, decide on handling strategies, and direct the dog through the course, with precision and speed equally important. Many strategies exist to compensate for the inherent difference in human and dog speeds and the strengths and weaknesses of the various dogs and handlers.

Because each course is different, handlers are allowed a short walk-through before the competition starts. During this time, all handlers competing in a particular class can walk or run around the course without their dogs, determining how they can best position themselves and guide their dogs to get the most accurate and rapid path around the numbered obstacles. The handler tends to run a path much different from the dog's path, so the handler can sometimes spend quite a bit of time planning for what is usually a quick run.

The walk-through is critical for success because the course's path takes various turns, even U-turns or 270° turns, can cross back on itself, can use the same obstacle more than once, can have two obstacles so close to each other that the dog and handler must be able to clearly discriminate which to take, and can be arranged so that the handler must work with obstacles between himself and the dog, called layering, or at a great distance from the dog.

Printed maps of the agility course, called course maps, are often made available to the handlers before they run, to help the handlers plan their course strategy. The course map contains icons indicating the position and orientation of all the obstacles, and numbers indicating the order in which the obstacles are to be taken.

Each dog and handler team gets one opportunity together to attempt to complete the course successfully. The dog begins behind a start line and, when instructed by his handler, proceeds around the course. The handler typically runs near the dog, directing the dog with spoken commands and with body language (the position of arms, shoulders, and feet).

Because speed counts as much as accuracy, especially at higher levels of competition, this all takes place at a full-out run on the dog's part and, in places, on the handler's part as well.

Scoring of runs is based on how many faults are incurred. Penalties can include not only course faults, such as knocking down a bar in a jump, but also time faults, which are the number of seconds over the calculated standard course time (SCT), which in turn is determined based on the competition level, the complexity of the course, and other factors.