Tomonaga may refer to:
- Jacobo Kyushei Tomonaga (1582-1633), a Japanese priest in the Dominican Order of the Catholic Church
- Minamoto no Tomonaga (1144-1160), a Minamoto clan samurai of the late Heian period
- Sin-Itiro Tomonaga (1906-1979), a Japanese physicist and Nobel Prize winner, influential in the development of quantum electrodynamics
- Luttinger liquid, also known as Tomonaga-Luttinger liquid, a theoretical model describing interacting fermions in a one-dimensional conductor