A scooter is a two-wheeled motor vehicle with a step-through frame. Many modern scooters have their engines located forward of the seat and affixed to the frame (e.g. Yamaha T-Max 500, Suzuki Burgman 650, Gilera GP800).

The classic scooter design features a step-through frame and a flat floorboard for the rider's feet. This design is possible because the scooter engine and drive system, transferring power to the rear wheel, is either attached to the rear axle or under the seat. In contrast to a frame mounted motorcycle engine, this front-hinged arrangement allows the engine to swing vertically in conjunction with the motion of the rear wheel. Older Vespas, most vintage scooters, and some newer retro models have axle mounted engines with a manual transmission with the gear shift and clutch controls built into the left handlebar. Most newer scooters use a Continuously Variable Transmission (CVT).

A typical mid-1980s "twist and go" scooter.In contrast to most motorcycles, scooters generally feature bodywork, including a front leg shield and body that conceals all or most of the mechanicals. There is often some integral storage space, either under the seat, built into the front leg shield, or both. Most modern motor scooters have smaller wheels than motorcycles, between eight and 12 inches (20-28 cm) in diameter (though maxi- and big-wheel scooters may have larger wheels). Most scooters have smaller engines than motorcycles (between 30 cc and 250 cc with a single cylinder, though larger models have twin cylinder 400 to 650 cc. motors). Most jurisdictions have no legal definition for "scooter". In general, 50 cc and under scooters are classified in most states and countries as a moped and are subject to reduced safety restrictions and licensing fees. Scooters above 50 cc are generally legally considered motorcycles, though some states have an in-between definition for motorized bike for scooters and motorcycles between 50 and 150 cc.

Until recently, most modern motor scooters came with air cooled two-stroke cycle engines with automatic two-stroke oil injection although some of the higher spec small ones and large ones are water cooled such as the Honda FC50 or the 2002 Yamaha YQ50s. Scooters increasingly have four-stroke engines to meet stricter emissions controls. Trends world-wide have seen new variations on the classic scooter. A common variation, the 'big-wheel' or commuter-style scooter features wheels as large as a motorcycle. Popular models of the commuter-style bike include the Aprilia Scarabeo models, the Piaggio Liberty/LT models, and the Taiwanese Kymco People models.

High-end scooter models now include comprehensive technological features including cast aluminum frames, engines with integral counter-balancing, and cross-linked brake systems. Some of these modern high-end scooters also come with comfort features such as windshields, heated hand grips and full instrumentation (including clock or outside temperature gauge.)

High-powered electric road scooters are on the horizon now that small electric motorcycles like the e-max and the eGO have been released.

In an effort to reduce emissions, there are now LPG powered scooters that run on LPG rather than petrol or diesel.

• History of the Motor Scooter
• Popularity of the Motor Scooter
• Maxi-Scooters
• Scootering Terms