The paper describes the conjunction tbət, a causal marker in Cambodian. Some aspects of its history and its functioning in Middle and Modern Cambodian are considered. Although there is no consensus as to the origins of this conjunction, its genetic links to the Sanskrit (or Pali) word pada ‘footstep, trace, vestige, pretext’ are indisputable. Its first appearance in texts goes back to Middle Cambodian. In 17 ^th– 18 ^th century texts, it occurs as a major causal marker functioning as either a preposition or conjunction. The paper analyzes its use during that period based on 17 ^th century epigraphic inscriptions and on a classical didactic poem, Cbap Preah Riəcsɒmphiə. Further, I analyze numerous occurrences of tbət in the picaresque tale Rɯəŋ Thunɲcəj, composed in an archaic style similar to Middle Cambodian. In modern written Cambodian, tbət only occurs as a causal conjunction. Causal clauses introduced by tbət invariably follow the main clause, while those with other causal markers can either precede or follow the main clause. Tbət is mostly found in journalistic or scientific texts. Though the conjunction sometimes lends certain “archaic” flavor to the texts it appears in, its meaning is often fairly neutral and only serves to mark an official, bookish style of the writing. As a typological rarity, Modern Cambodian sometimes uses tbət to mark concession, with the concessive tbət-clauses preceding the main clause.