In American football, the boundary lines consist of the sidelines and end lines. Sidelines run the length of the field, while end lines mark the boundary at each end. The area between the end lines is the end zone, where touchdowns are scored.

The sidelines and end lines make up the boundaries on a football field. There are specific rules for what is considered in bounds and out of bounds. Typically, anything that is inside the boundary lines is considered in bounds, while anything that touches or goes beyond the boundary lines is considered out of bounds.