A developing nation is an undeveloped nation. Such countries may actually be developing, but the term is often used euphemistically to include those which are not.

Developing nations are in general countries that have not achieved a significant degree of industrialization relative to their populations, and which have a low standard of living. There is a strong correlation between this status and high population growth.

The United Nations allows each nation to decide for itself whether it will be designated as "undeveloped" or "devoloping" (though many economists and other observers ignore the UN rule about self-designation). To moderate the euphemistic aspect of the word "developing", international organisations have started to use the term "least developed countries" (LLDCs) for the very poorest nations which can in no sense be regarded as developing. That is, LLDCs is the poorest subset of LDCs.

Other terms sometimes used are lesser developed countries or less developed countries (LDCs); underdeveloped nations or undeveloped nations; third world nations; the South; or non-industrialized nations. Conversely, the opposite end of the spectrum is termed developed nations, first world nations, or industrialized nations.

Nations clearly assigned to this category include:

• Most nations of Africa
• Most nations of Asia, excluding Japan and the East Asian Tigers
• Most nations of South America, Central America, and the Caribbean