This thesis is concerned with expletive clauses in Dutch. An example of such a construction follows in (1). (1) Er loopt iemand op straat. There walks someone on street ‘Someone is walking in the street.’ In this sentence the expletive pronoun er ‘there’ is supposedly in subject position, while the lexical subject iemand ‘someone’ remains lower in the clause (see Wesseling 2018 for a more detailed view of subjecthood and the subject position in Dutch). This begs the question what the syntactic function of er is. We also find expletive er in wh-subject questions, as in (2). (2) Wie komt er? who comes there ‘Who is coming?’ The wh-subject wie ‘who’ is in subject position, again the question is why er needs to be present. In this thesis I investigate the syntactic function of er. I argue that the pronoun er has an articulated internal structure. Cardinaletti and Starke (1999) argue that pronouns can be divided into three types: strong pronouns, weak pronouns and clitic pronouns. Depending on their morphosyntactic behavior, pronouns can be categorized as one of these types. Furthermore, these different types of pronouns have a different internal structure. In Chapter 2, it is shown that er (and its variants) should be analyzed as a weak pronoun. Furthermore, daar ‘there’ and hier ‘here’, which can also be used as expletive pronouns, are categorized as strong pronouns. This thesis argues that the internal structure of er and daar ‘there’ is similar, to the extent that they each contain a locative feature. The expletive pronoun er is also used in impersonal passive constructions in Dutch, as we can see in (3). (3) Werd er gelachen? was there laughed ‘Was there laughing?’ An extensive survey under 671 informants showed that instead of er the pronoun daar ‘there’ can also be used in such constructions. In these impersonal passive sentences, there is no lexical subject available to satisfy the EPP (Extended Projection Principle, Chomsky 1981). Apparently, er and daar ‘there’ adhere to the EPP here. In Chapter 3, it is ...