In the United Kingdom and Ireland, a retained firefighter, also known as an RDS firefighter or on-call firefighter, is a firefighter who does not work on a fire station full-time but is paid to spend long periods of time on call to respond to emergencies through the Retained Duty System. Many have full-time jobs outside of the fire service. Retained firefighters are employed and trained by the local fire and rescue service.

When required to answer an emergency call, retained firefighters are summoned to the fire station by a radio pager (also known as an "alerter"). Once at the station, the crews staff the fire engine and proceed to the incident. Retained firefighters are therefore required to live or work near to the fire station they serve. This allows them to respond to emergencies within acceptable and strict attendance time targets set out by each fire service.

Typically, retained firefighters are employed in rural areas or in large villages, small towns or run a second or third appliance at full time stations as a backup crew. They provide cover to 90% of the area of the UK - there are 14,000 in England and Wales. Of the approximately 8,500 operational firefighters in Scotland, about 32% are retained. London Fire Brigade, West Midlands Fire Service and Greater Manchester Fire and Rescue Service are the only fire and rescue services in the UK that do not have any retained firefighters.

Unlike volunteer firefighters, retained firefighters are paid for attending incidents. Both volunteers and retained are paid an annual "retainer fee" for being on call, but only retained firefighters receive further pay for each emergency call they respond to. The Fire Brigades Union (FBU) and the Retained Firefighters' Union (RFU) represent the interests of retained firefighters across the country.