The basic features of the capitation tax center around the fact that it is assessed on the individual. For this reason, it is commonly called a "poll" or "head" tax. "Poll" is derived from the old Anglo-Saxon word for "head." It is still in use today to refer to election "polls" where "heads" are counted. The remaining features of the tax are variable, since the sort of taxes assessed on individuals can vary greatly, as can be found in Adam Smith's famous treatment, "The Wealth of Nations."
Any tax that is levied on the basis an individual's being or doing something is a capitation tax. Examples of a capitation tax are fees charged to get a drivers license or the income tax. An example of taxes that are not levied on individuals are tariffs or consumption taxes, since these are levied on objects, not people. Older forms of taxation were assessed on communes or households, and therefore, these were not levied on individuals as such. All head taxes are direct taxes, but not all direct taxes are head taxes.
Adam Smith, in Volume II, sections 138 to 146 of Book V, criticizes the capitation tax then used in England and France. It is used, so the famed economist writes, because it is easy. The state can collect from individuals quickly and easily. They are based on a census because this is the only way the state can ever predict what it will collect. The beauty of it is that the predictions are always identical to the results because there is no escaping this tax. Hence, Smith concludes, it has become popular in modern --- that is late 18th century --- states. Governments realized that they were losing money in exempting certain groups from taxation. Therefore, taxes were levied on people as people.
When Vladimir Putin took office in Russia in 2000 as president, one of his most important early acts was to institute a 13 percent flat tax on all Russian citizens with no exceptions. Everything you earned was taxed 13 percent whether you were rich or dirt poor. This was both to make tax payment easy --- as it had collapsed in the 1990s --- as well as to entice those trying to avoid taxes to pay this lower rate. All income was --- and is, as of 2011 --- taxed at this 13 percent rate. This is a classic use of the capitation method to ease, Smith argued, the collection of taxes for the increase of state power.