Bicycles are a two-wheeled means of transportation. Having been here since the nineteenth century, bicycles are still a chief mode of transportation today. Bicycles are simple and easy to handle, inexpensive, non-polluting, quiet, small and easy to maneuver. They can be used by anyone, from a 5-year-old to a 70-year-old. The bicycle works on the simple principle of pushing the wheels forward by driving the pedals in a circular motion. The pedals are connected to the wheels by an iron chain. A steering rod helps to keep the bike balanced. The main parts in a bicycle are: the main frame, the drive train, steering rod, the seat or seats, brakes and gears (optional). There are many kinds of bicycles, depending on the function, number of riders, construction, gearing, sport or means of propulsion.

Tandem bicycles are those that are powered by more than one person. They are also known as twins, or twin cycles. For these bicycles, the main parts like the steering rod, and wheels are similar to a regular bike, but they have more than one seat and pedals. Tandem bicycles are more sturdily built in order to take the weight of more people. They are made of stronger components. These days, the designing is also being made differently for more ease in operation. Tandem bicycles have similar speed levels as normal bikes, but a lot depends on the coordination among the riders. Most tandem bikes are being lightweight so as to reduce the burden on the riders.

The front rider in a tandem is known as the pilot, captain or steersman. The rear rider is the navigator, stoker or rear admiral. Some tandem bikes also allow independent pedaling and navigation by the rear driver. Tricycles and recumbent tandem bicycles are some kinds of tandem bicycles. Bicycles for more than 2 riders are known as: "triples" or "triplets," "quads" or "quadruplets," and "quints" or "quintuplets" for three, four or five riders. There are tandem bicycles that accommodate even 10 riders, although these are very rare. Tandem bicycles are also used in competitions like the Paralympics, for visually challenged people. The blind contestant would be the stoker while a fully sighted contestant would be the captain.