One of Star Trek's most enduring alien races, the depiction of the Romulans has changed little between their introduction in the classic original series episode Balance of Terror through to recent appearances in Deep Space Nine and Voyager.

Despite brokering a form of detente with many other races, the Romulan Empire remains a perpetual foe of the Federation. The Romulans resemble their distant cousins the Vulcans, but have developed a radically different culture that is not centred around logic. They are imperialistic, but little details are known about their society or home planet Romulus.

A century before the missions of Kirk and Spock's Enterprise, the Federation fought a war with the Romulans which resulted in the establishment of the Neutral Zone, a no-man's land in space that protects their territory. Perhaps the Romulans' most famous contribution to Trek lore is the cloaking device, a mechanism that allows their ships to travel unseen and undetected. The Federation relinquished the right to develop cloaking technology at the Treaty of Algeron, but it has nevertheless served as a useful plot device in many of Star Trek's greatest episodes. (See The Enterprise Incident, The Search Parts 1 and 2, Face of the Enemy, The Pegasus, Defiant.)

At present, Ambassador Spock is working covertly to bring peace between the Federation and the Romulans, evidently a very tricky task. (See the Next Generation episodes Unification 1 and 2).

The Romulans' most celebrated illicit export is Romulan Ale, a strong alcoholic beverage frequently imbibed by Mr Scott in his private quarters on the Enterprise, and possibly responsible for his eerie Canadian/Caledonian brogue.