A bypass is a road or highway that avoids or "bypasses" a built-up area, town, or village, to let through traffic flow without interference from local traffic, to reduce congestion in the built-up area, and to improve road safety. A bypass specifically designated for trucks may be called a truck route.

If there are no strong land use controls, buildings are often built in town along a bypass, converting it into an ordinary town road, and the bypass may eventually become as congested as the local streets it was intended to avoid. Petrol stations, shopping centres and some other businesses are often built there for ease of access, while homes are often avoided for noise and pollution reasons.

Bypass routes are often controversial, as they require the building of a road carrying heavy traffic where no road previously existed. This creates a conflict between those who support a bypass to reduce congestion in a built up area, and those who oppose the development of (often rural) undeveloped land. However, some of those in the bypassed city may also oppose the project, because of the potential reduction in city-centre business.