This chapter begins by outlining the history and development of Yiddish, the traditional vernacular of Ashkenazic Jews, and it discusses how Yiddish went from being a vibrant language spoken by millions to being an endangered minority language with only a fraction of its original speaker population – primarily as a result of the Holocaust. The chapter explains how Yiddish came to be spoken in Britain from the 1880s onwards, when large numbers of Ashkenazim fled there to escape poverty and pogroms, and it details the initial tensions and subsequent cooperation between different waves and generations of Yiddish-speaking newcomers (which entailed shifting attitudes towards the Yiddish language). The chapter then provides an overview of the past and current geographical distribution of Yiddish-speaking communities in Britain, with a focus on the main urban centres, and it explores especially London’s thriving Yiddish culture between the two World Wars. This is followed by a discussion of the linguistic consequences of contact between Yiddish and English speakers, and particularly borrowings from each language into the other. Throughout, differences are explained regarding the language use and intergenerational transmission patterns of Yiddish among Haredi as compared to secular communities.