The study aims at investigating the discourse marker "hasa" 'now' in Jordanian Arabic using relevance theory. The study also examined the grammaticalization of "hasa" and how it developed to be a discourse marker. The study also explored the functions of "hasa" in Jordanian Arabic. The data, which consisted of 500 tokens of "hasa" 'now,' were collected from Jordanian radio programs, personal communications, and interviews with native speakers of Jordanian Arabic. The study found out that "hasa" 'now' was developed from the phrase "hay [characters omitted] 'this hour' by the process of grammaticalization. The study also found out that the lexical meaning of "hasa" as an adverb meaning 'now' developed to be a discourse marker serving different functions. The study also showed that "hasa" limits the hearer to a possible interpretation of utterances, which helps the hearer to reach the optimal relevance.