Abstract The main aim of this chapter is to examine adverbial causal af-því-að-clauses in modern Icelandic. Semantically, we argue that af-því-að-clauses can be interpreted as eventuality-related, as evidential or as speech-act-related causal clauses. Syntactically, we show that af-því-að-clauses can be analyzed as central, peripheral or disintegrated adverbial clauses in the sense claimed by Haegeman (2010, 2012), Schönenberger and Haegeman (this volume), and Frey (2011, 2012, 2016). Based on Krifka (to appear) and Frey (2020, to appear, this volume), we assume af-því-að-clauses to be assertive clauses attaching – depending on their interpretation – as Tense Phrase, Judge Phrase or Act Phrase adjuncts. Essentially, we take interpretative differences to follow from the distinct attachment heights. Main arguments for this three part division are based on binding data, embeddability, movement restrictions, and clausal anaphora.