Optimates (ˈɒptɪməts; Latin for "best ones", optimas) and populares (ˌpɒpjʊˈlɛəriːz,-jə-,-ˈleɪriːz; Latin for "supporters of the people", popularis) are labels applied to politicians, political groups, traditions, strategies, or ideologies in the late Roman Republic. There is "heated academic discussion" as to whether Romans would have recognised an ideological content or political split in the label.
Among other things, optimates have been seen as supporters of the continued authority of the senate, politicians who operated mostly in the senate, or opponents of the populares. The populares have also been seen as focusing on operating before the popular assemblies, generally in opposition to the senate, using "the populace, rather than the senate, as a means [for advantage]".
References to optimates (also called boni, "good men") and populares are found among the writings of Roman authors of the 1st century BC. The distinction between the terms is most clearly established in Cicero's Pro Sestio, a speech given and published in 56 BC, where he framed the two labels against each other.
With the publication of the Römische Geschichte in the 1850s, the German historian Theodor Mommsen set the enduring and popular interpretation that optimates and populares represented political parties, which he implicitly compared to the German liberal and conservative parties of his own day. Mommsen's paradigm, however, has been criticised by generations of historians, first by Friedrich Münzer, followed by Ronald Syme, who considered that Roman politics was marked by familial and individual ambitions, not parties. Other historians have pointed to the impossibility of applying such labels to many individuals, who could pretend to be popularis or optimas as they saw fit; the careers of Drusus or Pompey are for example impossible to fit into one "party". Ancient usage was also far from clear: even Cicero, while linking optimates to Greek aristokratia (ἀριστοκρατία), also used the word populares to describe politics "completely compatible with.