In cricket, the boundary is the perimeter of a playing field. It is also the term given to a scoring shot where the ball is hit to, or beyond, that perimeter, which generally earns four or six runs for the batting team.

Briefly, if the ball is struck by the batter and rolls or bounces over the boundary (or just touches it) it is known as a "four", and scores four runs, whereas if it flies over (or touches) the boundary, without touching the ground before that, it is called a "six", and scores six runs. There are rules covering every possible situation, including the fairly common one when a fielder is in the air beyond the boundary when they catch or strike the ball with their hand or another part of the body.

The boundary is the edge of the playing field, or the physical object (often a rope) marking the edge of the field. In low-level matches, a series of plastic cones or flags are sometimes used. Since the early 2000s, the boundaries at professional matches are often a series of padded cushions carrying sponsors' logos strung along a rope. If one of these is accidentally moved during play (such as by a fielder sliding into the rope in an attempt to stop the ball) the boundary is considered to remain at the point where that object first stood. The boundary is at least 195 feet (59 m) from the centre of the field in men's international cricket, and at least 180 feet (55 m) from the centre of the field in women's international cricket.

When the cricket ball is inside the boundary, it is live. When the ball is touching the boundary, grounded beyond the boundary, or being touched by a fielder who is himself either touching the boundary or grounded beyond it, it is dead and the batting side usually scores four or six runs for hitting the ball over the boundary. Because of this rule, fielders near the boundary attempting to intercept the ball while running or diving often flick the ball back in to the field of play rather than pick it up directly, because their momentum could carry them beyond the rope while holding the ball. They then return to the field to pick the ball up and throw it back to the bowler.

A law change in 2010 declared that a fielder could not jump from behind the boundary and, while airborne, parry the ball back on to the field.

A boundary is the scoring of four or six runs from a single delivery, with the ball having left the field, and its first bounce having occurred either entirely within the playing field (in the case of four runs) or not (six runs); these events are known as a four or a six, respectively.

Occasionally, there is an erroneous use of the term boundary as a synonym for a "four". For example, sometimes commentators say such as "There were seven boundaries and three sixes in the innings." The correct terminology would be "There were ten boundaries in the innings of which seven were fours and three were sixes."^{[citation needed]}

When this happens the runs are automatically added to the batsman's and his team's score and the ball becomes dead. If the ball did not touch the bat or a hand holding the bat, four runs are scored as the relevant type of extra instead; six runs cannot be scored as extras, even if the ball clears the boundary, which is in any case extremely unlikely.