Commonwealth (the territories belonging today partly to Poland, Lithuania and Belarus)is relatively little known and described in scholarly Polish history literature. This fact results mainly from the lack of available historical sources. The document entitled ‘German Reign in Grodno and its Vicinity’, which dates from May 1917, provides us with considerable amount of precious information about the situation of the Poles in the German zone subordinated to Ober Ost administration. The ruthless economic exploitation, obstruction of the organization of Polish education were typical of German authorities. The document also presents data on the ethnic composition of the area and political activity. The paper was prepared by Polish activists from Grodno and sent to the Supreme national committee in Krakow.