Using information from the books as well as onscreen Trek:
The Romulan Star Empire is an oligarchic society with a strict caste system, ruled by noble families whose members often gain seats in the Imperial Senate. The Senators aim to represent their constituants honourably, although backstabbing, power struggles and mutual suspicion often get in the way. Still, the Senators usually represent the views and concerns of the people they represent, or at least noble families in their constituency. The Senate is led and organized by a Proconsul, while the Praetor judges and presides from his seat in the Senate Chamber. The Praetor is politically the most powerful, the proconsul essentially his or her second in command. The Emperor or Empress is a spiritual figurehead who wields considerable power but less than the Praetor and leading Senators. The orders of priests serve the Emperor/Empress. The Praetor commands the military and the Tal Shiar. Leading senators have seats on the Continuing Committee, the senatorial oversight council led by the Praetor. The Chair of the Tal Shiar usually has a seat on the CC, but not always. Only full-blooded Romulans are true citizens of the Star Empire. Citizens have codified legal rights, such as the opportunity to make an official Statement when put on trial by the legal system. Personal honour is highly important, but sadly the paranoia of the Tal Shiar makes many citizens fearful to question the government. As a stereotype, Romulans are nationalistic and xenophobic. Self-reliant and proud after having survived exile from Vulcan and tamed a new world, they believe it is their destiny to rule the stars, at least traditionally. After the Coalition of Planets (later UFP) and Klingons prevented expansion from continuing in certain directions, Romulan history became a string of long periods of isolation punctured by brief periods of cold war, scheming and dischord-sowing. The 2360s (TNG) was the latest of these careful-aggressive periods. The Romulan Star Empire is large and far more varied than those in the Federation think.