In Persian, the word ‘ke’ has a variety of grammatical functions. It functions as ‘a relative pronoun’, ‘a complementizer’, ‘a conjunction meaning when’, and ‘a conjunction meaning because’. In addition to the above mentioned grammatical functions, it has a different functional behaviour. It can be used after any constituent in a sentence—NP, AdjP, PP, and VP—and it can also be used after subject, direct object, indirect object, verb, comparative adjective complement, subject complement, object complement, different adjuncts, negative adjunct, and non-verbal part of compound verb. In this functional role, ‘ke’ is used in order to focalize the constituent and make it prominent. If it is deleted, the sentence remains grammatical and its propositional meaning doesn't change, while its information structure regarding prominence/focus alters. It is generally believed that in order for an element to be focalized, it is necessary to be preposed to the beginning of the sentence. This study shows that focalization occurs in situ; that is, in Persian, through the use of ‘ke’ as a focus marker, elements can receive prominence in situ and any movement to the beginning of the sentence is just for topicalization.