Lightweight rowing (Lwt for short) is a special category of rowing where limits are placed on the maximum weight of competitors. The rationale is that larger, taller people have a small but significant physical advantage and tend to dominate the sport. Having a lightweight category gives average sized individuals the ability to compete against their peers, but rowers who are tall and thin generally have an advantage over those who are shorter but broader.
At international level for crew boats the limits are:
- Men: Crew average 70 kg (154.3 lb) - no rower over 72.5 kg (159.8 lb)
- Women: Crew average 57 kg (125.6 lb) - no one over 59 kg (130.0 lb)
For single sculls the limits are 72.5 kg and 59 kg for men and women respectively.
According to FISA, this weight category was introduced "to encourage more universality in the sport especially among nations with less statuesque people".
The first lightweight events were added to the World Championships in 1974 for men and 1985 for women. Lightweight rowing was added to the Olympics in 1996 but this came under threat in 2002 when the Programme Commission of the IOC recommended that, outside combat sports and weightlifting, there should not be weight category events. The Executive Board overturned this recommendation and lightweight rowing continues at the Olympics. There are three Olympic-class lightweight events: Men's Coxless Fours, Men's Double Sculls and Women's Double Sculls. The World Championships include lightweights' events for all classes of crew, and in Olympic years a reduced World Championship regatta includes all events that are not represented at the Olympics.
Top lightweight crew teams can go faster than other heavyweight teams. For example, at the 2010 Head of the Charles Regatta, the winner of the Lightweight Eights Men race (Princeton University) would have placed 5th in the Championship Eights Men race, ahead of Deutscher Ruder Verband (a U-23 German team), Cornell University, University of Wisconsin and Brown University. And at the 2012 Head of the Charles Regatta, the winning time in the Lightweight Eights Men race of 14:35.71 (Harvard) was faster than the winning time in the Championship Eights Men race (14:37.27, University of Washington).
Lightweight rowing is often denigrated as being "lesser" than its heavyweight counterpart, but is in reality a fairly different sport, relying much more on ideal body composition and technique than raw strength.
United States 
At the collegiate level, many larger American Division I schools, unlike their UK counterparts, can field between one and three lightweight boats for both men and women. In recent years the practice of juniors training down to a weight has been questioned as low BMI has been linked to health and growth problems in adolescents.
In both lightweight men's and lightweight women's collegiate rowing, competition at the school-funded 'Varsity' level is small but fiercely competitive; the de facto national championship for both disciplines is the Intercollegiate Rowing Association Championship held each year on the Cooper River in New Jersey on the weekend after Memorial Day. However, several club rowing programs (e.g., California Lightweight Crew), which receive minimal or no school funding, consistently field lightweight crews that compete for equivalent titles at the Dad Vail Regatta on the Schuylkill River in Philadelphia, and, most recently, at the American Collegiate Rowing Association Championships.
In the U.S. Collegiate category, the following limits apply as of spring 2011:
- Freshman Men: no rower over 160 lb.
- Varsity Men: no rower over 160 lb.
- Varsity Women: no rower over 130 lb.
In the Junior category, the following limits apply as of spring 2011:
- Men: No rower over 160 lb.
- Women: No rower over 130 lb.
- Lusky A, Barell V et al. (1996). "Relationship between Morbidity and Extreme Values of Body Mass Index in Adolescents". International Journal of Epidemiology 25 (4): 829–34. doi:10.1093/ije/25.4.829. PMID 8921463.
- Kanade AN, Joshi SB, Rao S. (1999). "Undernutrition and adolescent growth among rural Indian boys.". Indian Paediatrics 36 (2): 145–56. PMID 10713808.
- Fight In The Dog — Coverage of US women's collegiate lightweight rowing