Westphalia (; German: Westfalen [vɛstˈfaːlən]; Low German: Westfalen [vεs(t)ˈfɔːln]) is a region of northwestern Germany and one of the three historic parts of the state of North Rhine-Westphalia. It has an area of 20,210 square kilometres (7,800 sq mi) and 7.9 million inhabitants.

The territory of the region is almost identical with the historic Province of Westphalia, which was a part of the Kingdom of Prussia from 1815 to 1918 and the Free State of Prussia from 1918 to 1946. In 1946, Westphalia merged with North Rhine, another former part of Prussia, to form the newly created state of North Rhine-Westphalia. In 1947, the state with its two historic parts was joined by a third one: Lippe, a former principality and free state.

The seventeen districts and nine independent cities of Westphalia and the single district of Lippe are members of the Westphalia-Lippe Regional Association (Landschaftsverband Westfalen-Lippe).

Previous to the formation of Westphalia as a province of Prussia and later state part of North Rhine-Westphalia, the term "Westphalia" was applied to different territories of different sizes such as the western part of the ancient Duchy of Saxony, the Duchy of Westphalia or the Kingdom of Westphalia. The Westphalian language, a variant of the Low German language, is spoken beyond modern Westphalia's borders in neighbouring southwestern Lower Saxony and northwestern Hesse.