Civics

§ Civics represent the various forms of government available in Civilization IV. Are you a despot or a king, a democratically-elected ruler or a theocrat? Does your civilization have open markets or closed? Do you have trial by jury, or trial by fire? These and other possibilities are available to you.
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Effects in Play

§ The civics you choose to employ have a great effect upon the character and success of your civilization. Some civics increase your cities' productivity. Others increase their wealth. Some civics make it easier to create and maintain standing armies. Others help you to export your religions to other nations. There are no "best" civics in the game: all are potentially very useful in different situations.
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The Civics Screen

§ Go to the Civics Screen to review your current civics, to see which other civics are available to you, and to learn about other as-yet undiscovered civics.
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Acquiring Civics

§ You begin play with the most primitive civics: despotism, tribalism, and so forth. You acquire other civics through technological advances: the Hereditary Rule civic requires that your civilization master the Monarchy technology, for example, while Mercantilism requires Banking. (In addition, the Pyramids wonder makes all "government" civics available.)
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Categories of Civics

§ There are five different categories of civics, each controlling a certain aspect of your civilization: Government, Legal, Labor, Economy, and Religion.
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Upkeep

§ Each civic type has an "upkeep" cost associated with it: no upkeep, low upkeep, medium upkeep, and high upkeep. This represents the relative amount of gold that your civilization must pay each turn to employ that civic. In general, the more useful a civic is, the higher its upkeep. The actual cost in gold per turn of civics varies according to the size of your civilization: the more cities you have and the larger your population, the higher the upkeep cost for any and all civics.
§ If you are considering changing a civic, go to the Civics Screen. Check the Upkeep/Turn value on this screen - it represents your current ongoing civic outlay - then click on the civic you are considering. The Upkeep/Turn value will change to show what your upkeep will become if you change to that civic.
§ Be careful about changing over to civics with high upkeep costs; they are often powerful, but can put a real strain on your treasury. Some civics may be desirable simply because they have no upkeep cost!
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Changing Civics

§ When you acquire a new civic, a screen will pop up asking if you want to change civics. At any other time you want to change civics, you need to go to the Civics Screen by clicking on the icon in the top-right corner of the screen. Once on the Civics screen, click on the civic or civics you want to change to, then click on the "Revolution" button in the bottom-right corner. You may experience a period of "anarchy" (see below); when that passes you will be employing your new civics. (If you decide to keep things as they are and not change any civics, click on "Exit Screen" rather than "Revolution.")
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Revolution

§ Changing civics can be difficult for your loyal citizens, particularly if you are changing multiple civics at once. Your civilization may undergo a number of turns of "anarchy," during which chaos will reign: your citizens will cease gathering food, treasure, and production materials, and your cities will halt production and your income may well plummet precipitously. Your units will still respond to orders. Eventually things will settle down and return to order. When contemplating changing civics, go to the Civics Screen and click on the civics you would like to change to. The "Turns for Revolution" display will tell you how long the anarchy will last once you begin the Revolution.
§ Incidentally, certain civilizations are immune from anarchy: they can change civics any time they want without suffering any disruption.
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Delay Period

§ There is a delay period after changing civics before you can carry out another revolution. Your citizens can only change from one system of rule to another so often! Be aware before changing civics that you will have to wait a couple turns before being able to switch them again, should you not like the result.