Osogovo (
Bulgarian and
Macedonian Cyrillic: ) or
Osogovska Planina (Осоговска планина
or Осоговски Планини) is a mountain and ski resort between southwestern
Bulgaria (
Kyustendil Province) and northeastern
Republic of Macedonia, (
Kočani and
Kriva Palanka municipalities). It is about long and wide, the highest peak being
Ruen (Руен) at 2251 m, which constitutes the main orthographic knot on the very border between Bulgaria and the Republic of Macedonia. The steepest slope of the mountain is in the west, stretching down from Carev Vrv (Царев Врв; "Tsar's Peak").