Gambier Islands - French Polynesia, August 2011

A paddle is a tool used for pushing against liquids, either as a form of propulsion in a boat or as an implement for mixing.

Marine propulsion is the mechanism or system used to generate thrust to move a ship or boat across water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting a motor or engine turning a propeller, or less frequently, in jet drives, an impeller. Marine engineering is the discipline concerned with the design of marine propulsion systems.

Steam engines were the first mechanical engines used in marine propulsion, but have mostly been replaced by two-stroke or four-stroke diesel engines, outboard motors, and gas turbine engines on faster ships. Nuclear reactors producing steam are used to propel warships and icebreakers, and there have been attempts to utilize them to power commercial vessels. Electric motors have been used on submarines and electric boats and have been proposed for energy-efficient propulsion. Recent development in liquified natural gas (LNG) fueled engines are gaining recognition for their low emissions and cost advantages.

Human-powered watercraft are watercraft propelled by human power. The three main methods of collecting human power are directly from the hands or feet, through the hands with oars, paddles, or poles or through the feet with pedals and a crank or treadle. While most human-powered watercraft use buoyancy to maintain their position relative to the surface of the water, a few, such as human-powered hydrofoils and human-powered submarines use hydrofoils, either alone or in addition to buoyancy.

Paddling with regard to watercraft is the act of manually propelling a boat using a paddle. The paddle, which consists of one or two blades joined to a shaft, is also used to steer the vessel. The paddle is not connected to the boat (unlike in rowing where the oar is connected to the boat).

Human-powered transport is the transport of person(s) and/or goods using human muscle power. Like animal-powered transport, human-powered transport has existed since time immemorial in the form of walking, running and swimming. Modern technology has allowed machines to enhance human-power.

Although motorization has increased speed and load capacity, many forms of human-powered transport remain popular for reasons of lower cost, leisure, physical exercise and environmentalism. Human-powered transport is sometimes the only type available, especially in underdeveloped or inaccessible regions.

In the transport sector, walking and cycling transport are often grouped together under active transport, comparing to such other transport forms as public transport, or freight transport.^{[citation needed]}