A scooter is a two-wheeled vehicle with a step-through frame in which the rider sits without straddling any part of the engine.
Most modern motor scooters have smaller wheels than motorcyles, between 8 and 12 inches (20-28 cm) in diameter (though maxi- and big-wheel scooters may have larger wheels). The scooter engine is usually found under the seat with a continuously variable transmission transferring power to the rear wheel, often in a front-hinged arrangement that allows the rear of 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 a manual transmission with the gear shift and clutch built into the left handlebar.
In contrast to most motorcyles, scooters generally feature bodywork, including a front leg shield and body that conceals all or most of the mechanicals. The classic scooter design features a step-thru frame and a flat floorboard for the rider's feet and often includes some integral storage space, either under the seat, built into the front leg shield, or both.
Most scooters have smaller engines than motorcycles (between 30 cc and 250 cc with a single cylinder, though some models have twin cylinder 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 50cc 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 2-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.)
Another trend sees larger scooters, called maxi-scooters, with engines ranging in size from 250 cc up to 650 cc. This trend began in 1986 when Honda introduced the Fusion/Helix/CN250, and continued with the 1999 introduction of the Suzuki Burgman 400. Piaggio, Yamaha, Aprilia, Kymco and others have since introduced scooters with engine displacements ranging from 400 to 650cc. Honda's PS250 or Big Ruckus defies commons scooter classification in that it's "step-thru" is high and the bike features no bodywork but rather a motorcyle-like exoskeleton.
This trend toward larger, more powerful scooters with fully automatic transmissions is matched by an emerging trend in motorcyle design that foreshadows automatic transmission motorcycles with on-board storage.
Scooters trace their ancestry back to the USA, where Cushman and Salsbury created some of the first motorized two wheelers with the traits that have come to embody scooters. Salsbury produced the first automatic scooter with a Continuously Variable Transmission (CVT). Cushman's light, compact, and rugged scooters were used by the United States military as ground vehicles for paratroopers during World War II. The Vespa, originally manufactured by Piaggio in post-WWII Italy, quickly popularized motor scooters in places where inexpensive transportation was in dire need. Constructed using aircraft design and materials it redefined the vehicle type for 35 years. Despite Vespa's dominance of the scooter market, they were not without competition. Lambretta offered models that rivaled those in the Vespa product line. In the 1980s new versions of scooters began to be released and become popular, especially in Japan and Far-East Asia. This styling of scooters began to reflect that of larger, sporty, higher-performance motorcycles of the time and the trend has continued to the current day. With the release of the Honda Ruckus, new trends towards dirt-bike scooters are just beginning. The classic styling of the Vespa has never lost its popularity, however and remains the most popular and most imitated scooter design. Almost all manufacturers now carry both a classic/retro model and a sporty/modern model.
In many parts of the world, such as Europe and Asia, motor scooters are a popular form of urban transportation due to their size, fuel-efficiency, weight, and typically larger storage room than a motorcycle. In many localities, certain road motor scooters are considered by law to be in the same class as mopeds or small motorcycles and therefore they have fewer restrictions than that of larger motorcycles.
In the last few years, new technology has emerged. Fuel-injected scooters are very efficient and durable. Aprilia released the SR Ditech in 2000. The fuel consumption of this direct injection scooter is 1 liter of fuel for 50 kilometers of driving. Later on, more brands, such as Derbi and Peugeot, started using direct injection systems for their scooters. Due to new environmental laws, scooters had to change because the Euro3 standard allows only four-stroke engines. Some scooter drivers don't agree this is a good solution because they are used to two-stroke motors.
Scootering is the hobby of riding, restoring, and repairing motor scooters. In recent decades, collecting vintage motor scooters has become a popular hobby. Good examples of collectible scooters are european scooters like Vespas, Lambrettas, Heinkels, American scooters like Cushmans and Powells, and Japanese scooters like Fuji Rabbits and Mitsubishi Silver Pigeons.
In the UK from the 1960s to the present day, members of youth subcultures such as the Mods and Skinheads ride customized Vespas and Lambrettas, some adorned with many extra mirrors and chrome parts. The scootering scene has spread to other countries as far away as Australia, Japan, and the United States. All around the world people continue to gather their vintage scooters at rallies nearby, far away and in between, one or more scooter rallies are held every weekend of the year. A calendar of scooter rallies can be found on the Scoot.net Calendar.
Scooter Rally: An overnight event where scooter enthusiasts from various areas gather in one spot and which may be comprised of multiple meets, swap meets, rides, parties, and concerts. Some people may have a run leading to it. The Garden City Rally held every Victoria Day in Victoria British Columbia is the longest continuously running scooter rally in North America.
Scooter Meet: A single-day event where people from various areas gather in one spot. A meet may or may not have a ride leading to/from it.
Ride: A single-day event where people from a single area ride together.
- BSA 'Sunbeam' scooter
- Heinkel 'Tourist' scooter
- Maico 'Maicoletta' scooter
- Piaggio (made/makes Vespa)
- Triumph 'Tigress' and 'Tina' Scooters
- United Motors Matrix scooter
- Zundapp 'Bella' Scooter
In recent years, collecting vintage motor scooters has become a popular hobby. A good example of a collectable scooter is a Cushman. These are large scooters that were built in Lincoln, Nebraska from 1936 until 1965. Some models are seven feet (2.1 m) long and weigh over 300 pounds (136 kg). Most are powered by the Cushman Husky engine, which is a cast iron flathead design. Cushmans usually have 8 horsepower (6 kW) or less, but some Cushman Eagles have an aluminum OMC engine with overhead valves and 9 horsepower (7 kW). 
The German word "Kabinenroller" for microcar means enclosed motor scooter.
The primary differences between road motor scooters and electric road scooters are the use of electric motors and their tendency to not be built for heavy road use. Small electric scooters are becoming popular in North American campgrounds and suburban areas, as well as with youth.