The work is concerned with the reconstruction of the phonemes of Proto-Malayo-Javanic, the last proto-language which is directly continued by the Sundanese, Javanese, Malay, and Madurese. Part one contains a lexicostatistical calculation of the degrees of relationship among the four languages and a brief description of the phonology and morphophonemics of each language. Part two is devoted to the reconstruction of Proto-Malayo-Javanic phonemes. It shows "inter alia" that evidence from Malayo-Javanic languages requires the reconstruction of a number of Proto-Malayo-Javanic phonemes which hitherto have not been reconstructed for proto-languages of higher order or the proto-language of highest order, i.e. Proto-Austronesian. The appendix contains the basic vocabulary lists for the four languages, a map showing previously assumed language boundaries separating Sundanese, Jakarta Malay, Javanese and Madurese, and a revised map showing language boundaries as revealed in the course of the research, as well as Sundanese dialect maps. An index of the Proto-Malayo-Javanic reconstructions follows.