Trailer may refer to:
- Trailer (vehicle), an unpowered vehicle pulled by a powered vehicle
- Baggage trailer, a large flatbed baggage trolley
- Bicycle trailer, a wheeled frame for hitching to a bicycle to tow cargo or passengers
- Boat trailer to carry small boats
- Horse trailer and other trailers designed to haul livestock
- Semi-trailer, a trailer without a front axle
- Travel trailer, or caravan, a type of recreational trailer designed to provide sleeping space
- Semi-trailer truck, the combination of a tractor unit and one or more semi-trailers
- Mobile home, a relocatable housing unit with wheels and a hitch.
- Portable classroom, a temporary classroom for schools with insufficient building capacity - not technically a trailer due to lack of wheels or hitch. This temporary shelter can be relocated with a trailer, but by definition, the structure itself is not a trailer.
- Construction trailer, relocatable temporary accommodation with wheels and hitch used for offices and building materials storage on construction sites.
- Trailer (computing), data appended to a main block of data to facilitate its processing
- Trailer (promotion), an advertisement, usually in the form of a brief excerpt or string of excerpts, for media work
- Teaser trailer, a truncated version of a trailer meant to "tease" an upcoming work