Who's asking: Therese Schulz, Herrsching, Germany
You'd think this would be a simple question with a straightforward answer, but it's not. It varies, it depends on whom you ask, and it depends on how you define "country."
For our purposes, let's define "country" the way international law does, meaning a geographic territory with its own government whose boundaries are recognized by other countries, and which represents itself independently before international organizations. By this definition, Scotland, Wales and Northern Ireland are not countries; nor is Puerto Rico.
Under this definition, the world has 192, 193, or 194 countries. The United Nations has 192 member countries. The United States recognizes ambassadors from 193 countries; the extra one is Vatican City, which is not a member of the U.N. Some Chinese nationalists argue that the true number is 194, which includes Taiwan. The U.S. does not officially recognize Taiwan as a separate country, but this is diplomatic weaselry to appease mainland China.
So if you ask me, I say the number is 194; if you ask your teacher, she'll probably say 193. Remember, too, that there are at least half a dozen "wars of national liberation" being fought around the world at any given time -- if you ask this question again next year, you might get a different answer.