The Tax Rate is the player-controlled option for the amount of 
Gold collected from each Worker and Farmer in every settlement in your empire. The tax rate is directly related to citizen unrest, with higher levels of taxes causing higher levels of unrest.
Tax Rate can be changed using the Tax Collector advisor under the Info button, or directly by pressing F7 from the overland map.
The tax-to-unrest ratio is 10% unrest per 0.5 , up to 30% unrest 1.5 gold. Starting at 2 the unrest increases by an additional 5% per each 0.5 , making the tax levels above 2 much more difficult.
Strategy[]
The higher levels of taxes cause much greater amounts of to be collected, supporting larger armies and speeding production. The unrest caused by high taxes can be offset by religious building like the shrine and temple. The increase in gold may be large enough to justify one or two rebels in a city, and the decreased 
production or 
food they would otherwise provide.
In a mixed-race empire, players may not be able to set the tax rate as high as they wish. Racial unrest between the ruling race (where the player's Fortress is located) and other races can push unrest to an unacceptably high level. Players should consider this when choosing their starting race, and in decisions to keep, raze, or abandon captured cities.
Players using powerful unrest reducing spells like Stream of Life, Just Cause and Gaia's Blessing may be able to set their tax rates exceptionally high.