Opportunism is the practice of taking advantage of circumstances – with little regard for principles or with what the consequences are for others. Opportunist actions are expedient actions guided primarily by self-interested motives. The term can be applied to individual humans and living organisms, groups, organizations, styles, behaviors, and trends.

The Moderates or Moderate Republicans, pejoratively labeled Opportunist Republicans, was a French political group active in the late 19th century during the Third French Republic. The leaders of the group included Adolphe Thiers, Jules Ferry, Jules Grévy, Henri Wallon and René Waldeck-Rousseau.