With an acknowledgment that there exists some disagreement around the whole "socialism vs. communism" question — more on that below — here is a list of the countries that today can be said to align with the communist ideology, at least insofar as they are run by a communist party of some stripe.
1. China
China — officially, the People's Republic of China — with over 1.4 billion inhabitants, is the world's second-most populous country. Its government is entirely ruled by the CCP, the Chinese Communist Party.
Today, while economic control is concentrated at the state level, various industries have undergone market-based reforms, and there is a level of private ownership, as well as some very wealthy individuals.
They are a far cry from a classless society, in other words, but are still thought of as a communist country.
2. Vietnam
Officially the Socialist Republic of Vietnam, this country of over 100 million inhabitants is another example of an economic system that's compatible with communism.
In Vietnam, the Communist Party of Vietnam is the only political party, and maintains fairly extensive control over the economy, with many state owned enterprises still operating. Since the 1980s, however, the economic system has become more mixed, with private ownership becoming more common.
3. North Korea
The Democratic People's Republic of Korea is also commonly referred to as a communist country. Political power is held exclusively by the Worker's Party of Korea, which is centered around the Kim family, despite its claims to being a democratic state.
The 26 million people of North Korea have long suffered from human rights abuses, severe shortages of basic necessities and very little contact with the outside world. Still, the extensive state ownership of the means of production has led to its association with the ideals of communism.
4. Cuba
Home to about 10 million people, the Republic of Cuba is an island nation in the Caribbean Sea. While the ruling communist party has held power since the 1960s, like many communist states, the economic system has become increasingly friendly to private enterprise, especially in recent years.
Cuba is also known for its impressive achievements in public health, despite being a relatively poor country.
5. Laos
The Lao People's Democratic Republic, like its neighbor Vietnam, is one of two countries in Southeast Asia committed to building a communist society. Like many communist governments, it has only one legally recognized party: the Lao People's Revolutionary Party.
Also like many present-day socialist countries, it has seen increased tolerance for market reforms and private property, especially in recent years.