Bohemia is the westernmost and largest historical region of the Czech lands in the present-day Czech Republic. Bohemia can also refer to a wider area consisting of the historical Lands of the Bohemian Crown ruled by Bohemian kings, including Moravia and Czech Silesia, in which case the region is referred to as Bohemia proper as a means of distinction.

Bohemia was a duchy of Great Moravia, later an independent principality, a kingdom in the Holy Roman Empire, and subsequently a part of the Habsburg Monarchy and the Austrian Empire. After World War I and the establishment of an independent Czechoslovak state, the whole of Bohemia became a part of Czechoslovakia, defying claims of the German speaking inhabitants that regions with German speaking majority should be included in the Republic of German-Austria. Between 1938 and 1945, these border regions were joined to Nazi Germany as the Sudetenland.

The remainder of Czech territory became the Second Czechoslovak Republic and was subsequently occupied as the Protectorate of Bohemia and Moravia. In 1969, the Czech lands (including Bohemia) were given autonomy within Czechoslovakia as the Czech Socialist Republic. In 1990, the name was changed to the Czech Republic, which became a separate state in 1993 with the breakup of Czechoslovakia.

Until 1948, Bohemia was an administrative unit of Czechoslovakia as one of its "lands" ("zeme"). Since then, administrative reforms have replaced self-governing lands with a modified system of "regions" ("kraje") which do not follow the borders of the historical Czech lands (or the regions from the 1960 and 2000 reforms). However, the three lands are mentioned in the preamble of the Constitution of the Czech Republic: "We, citizens of the Czech Republic in Bohemia, Moravia and Silesia…"

Bohemia had an area of 52,065 km² (20,102 sq mi) and today is home to approximately 6.5 million of the Czech Republic's 10.5 million inhabitants. Bohemia was bordered in the south by Upper and Lower Austria (both in Austria), in the west by Bavaria and in the north by Saxony and Lusatia (all in Germany), in the northeast by Silesia (in Poland), and in the east by Moravia (also part of the Czech Republic). Bohemia's borders were mostly marked by mountain ranges such as the Bohemian Forest, the Ore Mountains, and the Krkonoše, a part of the Sudetes range; the Bohemian-Moravian border roughly follows the Elbe-Danube watershed.