The optimates ("Best Men", singular optimas; also known as boni, "Good Men") were the traditionalist majority of the late Roman Republic. They wished to limit the power of the popular assemblies and the Tribunes of the Plebs, and to extend the power of the Senate, which was viewed as more dedicated to the interests of the aristocrats who held the reins of power. In particular, they were concerned with the rise of individual generals who, backed by the tribunate, the assemblies and their own soldiers, could shift power from the Senate and aristocracy. They were opposed by the populares.

Many members of this faction were so classified because they used the backing of the aristocracy and the senate to achieve personal goals, not necessarily because they favored the aristocracy over the lower classes. Similarly, the populares did not necessarily champion the lower classes, but often used their support to achieve personal goals.

The optimates favored the nobiles (noble families) and opposed the ascension of novi homines ("new men", usually provincials) into Roman politics. Cicero, a strong supporter of the optimates' cause, was himself a novus homo, being the first in his family to enter the Senate, and was never fully accepted by the optimates. During the Civil War of 49BC, Julius Caesar, of a respectable old family, contended against a Senate championed by Pompey the Great.