There is a short answer to how many national flags exist, and then there is the longer answer that starts as soon as you ask what counts as a nation.
The count of national flags
There are 195 recognized countries in the world, and each has its own national flag. That count comes from the United Nations: 193 member states plus 2 observer states, the Holy See and Palestine. The number gets more complicated once you include regions and territories that have their own flags but aren't recognized as independent nations.
Taiwan, for instance, is recognized by some countries but not by the United Nations. Puerto Rico is part of the United States and has its own flag. Add dependent territories, special administrative regions, and autonomous regions, and the total climbs well past 195.
Flags beyond national borders
National flags are only a fraction of the flags in use. There are state and provincial flags, city flags, organizational flags, and personal flags. In the United States alone, each of the 50 states has one. The same goes for the provinces of Canada, the states of Mexico, and regions in many other countries.
The symbolism and design of flags
A flag's design and colors usually carry meaning tied to the history and ideals of the place. The American flag, known as the Stars and Stripes, has 50 stars for the states and 13 stripes for the original colonies. Japan's flag, the Nisshoki or "sun-mark flag," is a red circle centered on white, standing for the sun. South Africa's flag is one of the most colorful in the world, designed to signify the coming together of different cultures after apartheid.
Individual colors tend to carry their own associations. Red often represents strength and valor, white peace and purity, and blue vigilance, perseverance, and justice.
A few things worth knowing
Nepal's flag is the only national flag that isn't quadrilateral. It's made of two stacked triangles.
Under Gaddafi's rule from 1977 to 2011, Libya flew a plain green flag, the only national flag of a single color with no design or insignia at all.
Some countries, including Spain and the United States, use different versions of the national flag for civilian, state, and military purposes.
Changing flags
Flags change as countries do. Mauritania added red stripes to its flag in 2017 to honor the sacrifices of its people. Canada adopted the maple leaf flag in 1965, moving away from a design that prominently featured the Union Jack.
The process of adopting a flag
Adopting or changing a national flag is a political process. It usually involves legislation, sometimes a referendum, and above all public sentiment. New Zealand held a referendum in 2016 on whether to change its flag, and the public voted to keep the original design.
So the count is 195 national flags, and many thousands more once you include regional, provincial, and organizational ones. Each carries the story of the place that flies it.