While it would appear to be a rather simple matter to determine how many countries there are in the world, it is in fact quite complex. This is due not only to the ever-shifting political landscape, but also because the term ‘countries’ is somewhat fluid and open to interpretation.
A narrow definition of what a country is might look at a well-established group — such as the United Nations — and take its list of recognized members. In the case of the United Nations, there are 193 recognized states, with 192 being members of the United Nations, and the Vatican City, which is a permanent observer with all rights of a member, save voting rights.
One could also take an established definition for what a state is, and find all states which match those criteria. The most widely-accepted definition is given by the Montevideo Convention, from 1933. By these guidelines, a state must have a government, be in a position to interact with other states diplomatically, have a defined territory, and possess a permanent population. A rough count of these states would place the number of countries in the world at 201. That includes the 193 states recognized by the United Nations, as well as eight additional states. These are the Western Sahara, Taiwan, Northern Cyprus, Somaliland, South Ossetia, Transnistria, Abkhazia, and Nagorno-Karabakh. These states meet the criteria set out by the Montevideo Convention, but are all in a struggle with another, larger state, for independence, and so far have not been formally recognized by the United Nations.
An even broader definition could include some states which have been recognized by a number of countries, but have either failed to establish a steady government, or have failed to receive recognition by enough fellow states to truly meet the criteria of the Montevideo Convention. By adding in states such as the Cook Islands, Palestine, or the Chechen Republic, one could get to a much greater number of countries in the world — somewhere in the range of 210-230.
Going even broader, one can include countries that are part of a larger country, sometimes referred to as constituent countries. One obvious example of this would be the countries of England, Scotland, Wales, and Northern Ireland — all making up the single country of the United Kingdom. In most counts of the countries in the world, these four countries are counted as one, but they could easily be counted as four instead. By including these sorts of countries there could be many hundreds, if not thousands, of countries in the world — especially if one were to start counting smaller states, such as California or Delaware in the United States, as independent in their own right.
Similarly, territories — such as the territory of Guam, a possession of the United States — are usually not counted in an official count, but are states by many criteria. These are referred to by the United Nations as Non-Self Governing Territories, and include an additional 16 territories.
So, how many countries are there in the world? 193 by the count of the United Nations. 193 also by the count of the United States Department of State. 201 by a tight interpretation of the Montevideo Conventions. Somewhere over 220 by a looser interpretation. And if we were to go by the number of countries that have their own domain suffix — such as .us for the United States, or .de for Germany — we would find 243. So there is no firm answer, but 193 is commonly accepted, and somewhere between 193 and 250 seems rather certain.