Croatia proper (Croatian: Hrvatska) is one of the four historical regions of the Republic of Croatia, together with Dalmatia, Istria, and Slavonia. It is located between Slavonia in the east, the Adriatic Sea in the west, and Dalmatia to the south. The region is not officially defined, and its borders and extent are described differently by various sources. In contemporary geography, the terms Central Croatia (Središnja Hrvatska) and Mountainous Croatia (Gorska Hrvatska) are used to describe most of this area, the former referring to the northeastern part and the latter to the southwestern part; the far western part is known as the Croatian Littoral; likewise the terms 'Zagreb macroregion' and 'Rijeka macroregion' can be used instead. Croatia proper is the most significant economic area of the country, contributing well over 50% of Croatia's gross domestic product. The capital of the Republic of Croatia, Zagreb, is the largest city and most important economic centre in Croatia proper.

Croatia proper comprises several smaller regions of its own: Lika, Gorski Kotar, Zagorje, Međimurje, the Croatian Littoral, Podravina, Posavina, Kordun, Banovina, Prigorje, Turopolje, Moslavina, and Žumberak. The region covers 28,337 square kilometres (10,941 square miles) of land and has a population of 2,418,214. Croatia proper straddles the boundary between the Dinaric Alps and the Pannonian Basin. The boundary of these two geomorphological units runs from Žumberak to Banovina, along the Sava River. The Dinaric Alps area is typified by karst topography, while the Pannonian Basin exhibits plains, especially in the river valleys—along the Sava, Drava, and Kupa—interspersed with hills and mountains developed as horst and graben structures. Lika and Gorski Kotar are part of the Dinaric Alps, and contain five out of eight mountains in Croatia higher than 1,500 metres (4,900 feet). Karst topography predominates in that area, resulting in specific landforms and hydrology because of the interaction of the karst and the region's watercourses—this is exemplified by the Plitvice Lakes. Most of the region has a moderately warm and rainy continental climate, although there is considerable seasonal snow at greater elevations. The region belongs almost exclusively to the Black Sea drainage basin and includes most of the large rivers flowing in Croatia.

The boundaries of Croatia proper were shaped by territorial losses of medieval Croatia to the Republic of Venice and the Ottoman conquest starting in the 15th century. In effect, Croatia proper loosely corresponds to what was termed reliquiae reliquiarum olim magni et inclyti regni Croatiae (the relics of the relics of the formerly great and glorious Kingdom of Croatia) and the subsequent Kingdom of Croatia within the Habsburg monarchy. The region contains most of the 180 preserved or restored castles and manor houses in Croatia, as it was spared any large-scale war damage throughout its history. Varaždin and Zagreb occupy prominent spots in terms of culture among the region's cities. The west of the region represents a natural barrier between the Adriatic Sea and the Pannonian Basin, and this, along with Ottoman conquest and resulting military frontier status, has contributed to the relatively poor development of the economy and infrastructure of that area.