This book establishes and applies a linguistic framework for the synchronic and diachronic analysis of multi-word discourse markers (MWDMs). The aim of this study is to examine in detail how MWDMs have developed out of their polysemous lexical counterparts. First, this study critically evaluates existing Grammaticalization and Pragmaticalization theories addressing both their strengths and drawbacks. In the following, a revised Pragmaticalization approach is developed. Considering three linguistic dimensions, this approach consists of six mechanisms: Discursivization & Scope Extension (semantic dimension), Syntactic Isolation & Acategorialization (syntactic dimension) and Consistency & Prosodic Accentuation (phonological dimension). Using data from the Oxford Etymological Dictionary and the TV Corpus, the study then applies these mechanisms to the MWDMs by the way, all the same and what is more. Providing a detailed corpus-informed analysis of these units, this book demonstrates the advantages of the suggested framework and consequently offers an innovative contribution to the field of linguistics.