The category of least developed countries is a social/economic classification status applied to roughly 40 countries around the world by political scientists and economists. Though sometimes LDCs is used as an abbreviation for "least developed countries", the abbreviation LLDCs is preferred to avoid confusion with "lesser developed countries".

However, the term is sometimes used synonymously with "lesser developed countries" or other synonyms of "lesser developed countries" such as "third world" nations, though the United Nations and the CIA World Factbook draw a distinction between "least developed countries" and "less developed countries"; the former is even less developed than the latter. Many contemporary scholars make careful note of the distinction, arguing that terms like "third world" are outdated or irrelevant.

As the name suggests, LLDCs are generally poor, underdeveloped countries, often marred by widespread conflict and political instability. Such countries are usually run by incompetent yet brutal dictatorships, and have very little democracy or freedom. They are commonly marred by ethnic clashes, often as a result of a lasting legacy of colonialism or Communist rule.

Current LLDCs include, among many others, Afghanistan, Bangladesh, Botswana, Chad, Laos, Lesotho, Mali, Sierra Leone, Sudan, Somalia, and Yemen.

See also: Newly industrialized countries