This chapter explores the research agenda and benefits of sociolinguistically oriented historical contact linguistics. It re-evaluates the contact scenario as it has been described in linguistic literature investigating Vienna in the second half of the nineteenth and the first decades of the twentieth century and re-assesses the contact explanation for phonological change in Viennese dialect, namely the so-called ‘Viennese e-confusion’ (Germ. Wiener E-Verwirrung). The chapter’s key proposition is that contact linguistics needs to account for variation in both the target and the source language. This has so far not been considered regarding language contact of Czech and German in Vienna during the late Habsburg rule. The current study provides evidence for rejecting the claim that the merger of /e/ and /ɛ/ in Viennese into a single phoneme /ɛ/ was induced by contact with Czech (cf. Kranzmayer 1953).