A bicycle trailer or tagalong is a wheeled frame with a hitch system that one attaches to rear end of their bicycle to easily transport cargo. Bicycle trailers frequently have some sort of fabric, plastic, or net covering to protect the contained cargo from the elements; whether that may be rain, wind, insects, sunshine, thievery, etc.

The frame is most often made out of either metal, wood, heavy plastic, or any combination of the three.

There are various different types of trailers available for the intended cargo:

Small children or infants can be passengers of the bicycle trailer, and for such purposes are trailers with padding, seat belts, rain proof covers, and wide-spaced wheels for the comfort and safety of the child.

Kayaks and canoes can be transported via a bike with a trailer specifically designed to be long, slender, and able to support the weight of the kayak or canoe.

General cargo trailers can be used to transport anything from water bottles to heavy tools, and the features of these mostly depend on the total weight of the intended cargo.