Sid Meier's Civilization III is a turn-based strategy game where the objective is to rule the planet with the civilization of the player's choice. Players control one of 15 historic civilizations (Aztecs, Egyptians, Russians, etc). Each civilization has its own particular strengths and weaknesses -- some are more scientific, for example, while others have stronger cultural or military attributes; also, each civilization has its own unique unit, and is more prone to certain forms of government while shunning some others.

Like in the previous titles in the series, the point of the game is to expand the influence of a civilization through resource management, conquest, or trade with other civilizations. As game time progresses from ancient times through the modern era, a civilization will acquire new technologies, which in turn enable interesting new abilities and enhanced power. Since there are several ways to win (military, diplomatic, or cultural), it is up to each player to determine how best to manage the division of labor.

The game includes some mechanics and features which were introduced in Sid Miere's Alpha Centauri, such as borders between civilizations and the aforementioned differences between each civilization's statistics. The advisors are now present in the upper right corner of the screen in relevant menus. Diplomacy has been expanded, with the ability to trade and even slightly haggle with other civilizations in a more detailed way. Other new additions include the great leader mechanic, war weariness amongst the population, and small wonders.