Sambahsa (constructed pronunciation: [samˈbaːsa]) or Sambahsa-Mundialect is an international auxiliary language (IAL) and worldlang devised by French linguist Olivier Simon. It is based on the Proto-Indo-European language (PIE) and has a relatively complex grammar. The language was first released on the Internet in July 2007; prior to that, the creator claims to have worked on it for eight years. According to a study addressing recent auxiliary languages, "Sambahsa has an extensive vocabulary and a large amount of learning and reference material".

The first part of the name of the language, Sambahsa, is composed of two words from the language itself, sam and bahsa, which mean 'same' and 'language', respectively. Mundialect, on the other hand, is a fusion of mundial 'worldwide' and dialect 'dialect'.

Sambahsa tries to preserve the original spellings of words as much as possible and this makes its orthography complex, though still kept regular. There are four grammatical cases: nominative, accusative, dative and genitive.

Though based on PIE, Sambahsa borrows a good proportion of its vocabulary from other language families, such as Arabic, Chinese, Indonesian, Swahili and Turkish.

Sambahsa's phonology has little to do with Proto-Indo-European phonology, though the majority of its vocabulary comes from PIE. The changes from PIE are not regular, since the creator of Sambahsa has tried to avoid homophones, which would have become common after the elimination of some PIE sounds like laryngeals or some aspirated consonants. Unlike some auxlangs like Esperanto, the orthography of Sambahsa is complex yet regular and consists only of the 26 letters of the basic Latin alphabet. This system was chosen to preserve the recognizability of words taken from West-European languages, where orthography plays a key role. For example, according to the rules of Sambahsa, bureau is pronounced as in French, and point as in English.

Sambahsa's phonemic inventory has 22 consonants and nine vowels (excluding the lengthened forms of these vowels). To help language learners, and because IPA symbols cannot be written with all keyboards, a special simpler system has been developed, called Sambahsa Phonetic Transcription, or SPT.

Compared to other conlangs, Sambahsa words are short, often as short as English words, and highly consonantic. This latter point is in accordance with the PIE background of Sambahsa, where roots have often a consonant-vocal-consonant structure.

Sambahsa's stress rules are complex but regular, and tend to follow what is often found in German or Italian. This predictability implies that all words with the same orthography are pronounced and stressed the same way as each other. Thus, for example, while German Präsident and Italian presidente are stressed on the "ent" syllable, Sambahsa president is stressed on the "i", since president can also mean "they preside", and a final "ent" never bears the stress. This regularity of accentuation can be compared with English president and to preside, two words that bear the stress on different syllables, though they share the same origin.