Indonesian or Bahasa Indonesia, based on the Riau version of Malay language, was declared the official language with the declaration of Indonesia's independence in 1945, following the 1928 "unifying language" declaration in the Indonesian Youth Pledge.

Most Indonesians, aside from speaking the national language, are often fluent in another regional language or local dialect (examples include Minangkabau, Sundanese and Javanese) which are commonly used at home and within the local community. Most formal education, as well as nearly all national media and other forms of communication, are conducted in Indonesian.

The Indonesian name for the language is Bahasa Indonesia. This term can sometimes still be found in written or spoken English. In addition, the language is sometimes referred to as "Bahasa" by English-speakers, though this simply means "language" and thus is also not an official term for the Indonesian language.

Indonesian is a normative form of the Malay language, an Austronesian (or Malayo-Polynesian) language which has been used as a lingua franca in the Indonesian archipelago for centuries. It was elevated to the status of official language with the Indonesian declaration of independence in 1945, drawing inspiration from the Sumpah Pemuda (Youth's Oath) event in 1928.
Because of its origins, Indonesian (in its most standard form) is mutually intelligible with the official Malaysian Malay.
 

However, it does differ from Malaysian Malay in some aspects, with differences in pronunciations, dictions, spellings, accents and vocabularies. These differences are mainly due to the Dutch and Javanese influences on Indonesian.

Whilst Indonesian is spoken as a mother tongue (first language) by only a small proportion of Indonesia's large population, over 200 million people regularly make use of the national language - some with varying degrees of proficiency. In a nation which boasts more than 300 native languages and a vast array of ethnic groups, the use of proper or 'good and correct' Indonesian (as opposed to Indonesian slang or regional dialects) is an essential means of communication across the archipelago. Use of the national language is abundant in the media, government bodies, schools, and universities, workplaces, amongst members of the Indonesian upper-class or nobility and also in many other formal situations.

Most native speakers of Indonesian would agree that the standard, correct version of the Indonesian language is rarely used in daily communication. One can find standard and correct Indonesian in books and newspapers, or listen to it when watching the news or television/radio broadcasts, but few native Indonesian speakers use formally correct language in their daily conversations.
 

While this is a phenomenon common to most languages in the world (for example, spoken English does not always correspond to written standards), the degree of "correctness" of spoken Indonesian (in terms of grammar and vocabulary) by comparison to its written form is noticeably low. This is mostly due to the fact that most Indonesians tend to combine certain aspects of their own local languages (eg. Javanese, Sundanese, Balinese, and even Chinese dialects) with Indonesian. The result is the creation of various types of 'regional' Indonesian, the very types that a foreigner is most likely to hear upon arriving in any Indonesian city or town.

The Dutch colonization left an imprint on the Indonesian language that can be seen alongside Malay, Portuguese was the lingua franca for trade throughout the archipelago from the sixteenth century through to the early nineteenth century. Indonesian words derived from Portuguese and Chinese origin.