Mennonite Plautdietsch (ISO 639–3: pdt) is a West Germanic (Indo-European) language belonging to the Low Prussian (Niederpreußisch) subgroup of Eastern Low German (Ostniederdeutsch), a continuum of closely related varieties spoken in northern Poland until the Second World War (Ziesemer 1924, Mitzka 1930, Thiessen 1963). Although its genetic affiliation with these other, now-moribund Polish varieties is uncontested, Mennonite Plautdietsch represents an exceptional member of this grouping. It was adopted as the language of in-group communication by Mennonites escaping religious persecution in northwestern and central Europe during the mid-sixteenth century, and later accompanied these pacifist Anabaptist Christians over several successive generations of emigration and exile through Poland, Ukraine, and parts of the Russian Empire. As a result of this extensive migration history, Mennonite Plautdietsch is spoken today in diasporic speech communities on four continents and in over a dozen countries by an estimated 300,000 people, primarily descendants of these so-called Russian Mennonites (Epp 1993, Lewis 2009).