Najd or Nejd (Arabic: نجد ‎, Naǧd), literally Highland, is the central region of the Arabian Peninsula.

The Arabic word nejd literally means "upland" and was once applied to a variety of regions within the Arabian Peninsula. However, the most famous of these was the central region of the Peninsula roughly bounded on the west by the mountains of the Hejaz and Yemen and to the east by the historical region of Bahrain and the north by Iraq and Syria.

Medieval Muslim geographers spent a great amount of time debating the exact boundaries between Hejaz and Nejd in particular, but generally set the western boundaries of Nejd to be wherever the western mountain ranges and lava beds began to slope eastwards, and set the eastern boundaries of Nejd at the narrow strip of red sand dunes known as the Ad-Dahna Desert, some 100 km (62 mi) east of modern-day Riyadh. The southern border of Nejd has always been set at the large sea of sand dunes known today as Rub' al Khali (the Empty Quarter), while the southwestern boundaries are marked by the valleys of Wadi Ranyah, Wadi Bisha, and Wadi Tathlith.