Even after more than 50 years of research, the origins of the Japanese and Korean languages remain controversial. In this presentation, we will discuss new evidence for the theory that Japanese and Korean descend from the same ancestor language, ‘proto-Korean-Japanese,’ forming a hypothetical Japano-Koreanic language family. In addition to lexical correspondences in core realms of vocabulary that build on previous comparative treatments (Martin 1966, Whitman 1985), we will discuss some close and interlocking morphological correspondences between the two languages, correspondences that are unlikely to be the result of chance or later borrowing. We will show that a strong set of core correspondences can be established between the morpho-lexicon of Japanese and that of Korean. These correspondences provide a more solid basis for a proof of common origin for these two languages than has previously been possible. We will conclude with a discussion of some implications that the Japano-Koreanic reconstruction has for the theory of Transeurasian.