Demand-responsive transport (DRT), also known as demand-responsive transit, demand-responsive service, Dial-a-Ride transit (sometimes DART), flexible transport services, Microtransit, Non-Emergency Medical Transport (NEMT), Carpool or On-demand bus service is a form of shared private or quasi-public transport for groups traveling where vehicles alter their routes each journey based on particular transport demand without using a fixed route or timetabled journeys. These vehicles typically pick-up and drop-off passengers in locations according to passengers needs and can include taxis, buses or other vehicles. Passengers can typically summon the service with a mobile phone app or by telephone; telephone is particularly relevant to older users who may not be conversant with technology.

One of the most widespread types of demand-responsive transport (DRT) is to provide a public transport service in areas of low passenger demand where a regular bus service is not considered to be financially viable, such as rural and peri-urban areas. Services may also be provided for particular types of passengers. One example is the paratransit programs for people with a disability. The provision of public transport in this manner emphasises one of its functions as a social service rather than creating a viable movement network.

DRT can be used to refer to many different types of transport. When taxicabs were first introduced to many cities, they were hailed as an innovative form of DRT. They are still referred to as DRT in some jurisdictions around the world as their very nature is to take people from point-to-point based on their needs.

More recently, DRT generally refers to a type of public transport. They are distinct from fixed-route services as they do not always operate to a specific timetable or route. While specific operations vary widely, generally a particular area is designated for service by DRT. Once a certain number of people have requested a trip, the most efficient route will then be calculated depending on the origins and destinations of passengers.

Share taxis are another form of DRT. They are usually operated on an ad hoc basis but also do not have fixed routes or times and change their route and frequency depending on demand.

Some DRT systems operate as a service that can deviate from a fixed route. These operate along a fixed alignment or path at specific times but may deviate to collect or drop off passengers who have requested the deviation.

DRT services are restricted to a defined operating zone, within which journeys must start and finish. Journeys may be completely free form, or following skeleton routes and schedules, varied as required, with users given a specified pick-up point and a time window for collection. Some DRT systems may have defined termini, at one or both ends of a route, such as an urban centre, airport or transport interchange, for onward connections.

DRT systems require passengers to request a journey in advance. They may do this by booking with a central dispatcher who determines the journey options available given the user's location and destination. Increasingly, the booking is via an app, which provides the interface to software that creates a schedule in real time; adjusting the schedule to accept (or reject) bookings as they come in. This provides an instant decision for the potential user, but at the cost of efficiency: each individual travel need is considered individually, potentially resulting in higher levels of idle time (when the schedule has gaps that are too short to allow an additional journey to be added) and "dead mileage" (driving empty between one drop-off and the next pickup) than might be expected from a schedule built by an experienced human operator.