Oman proper (Arabic: عُمان الوسطى ʿUmān al-Wusṭā) refers to a historical area within the present-day Sultanate of Oman. It lay inland from Muscat beyond the Jebel Akhdar (Green Mountains) and was centered on the city of Nizwa in the area of the current region of Ad Dakhiliyah. Along with Muscat and Dhofar, it was a constituent part of the Sultanate of Muscat and Oman, but with the 1970 palace coup, the term Oman alone was applied to the entire country.
Oman proper was ruled by Ibaditeimams who exercised spiritual and often temporal authority over the region. The Imamate is a thousand-year-old system of government pioneered by the Ibadi religious leaders of Oman, and is based upon the Islamic sharia. It governed parts or the whole of Oman and other lands for interrupted periods of time for over 1000 years. There were often tensions between these imams and the sultans of Muscat, and in 1913, the election of Salim ibn Rashid al-Kharusi as imam led to the Seeb Peace Treaty between Imamate of Oman (Arabic: إمامة عُمان Imāmat ʿUmān) with its capital at Nizwa and the Sultanate of Oman with its capital in Muscat. In 1954, a new imam, Ghalib bin Ali, defended the Imamate from attack from Muscat, after oil was discovered in his lands. Sultan Said Bin Taimur of Muscat with the help of the colonial British forces were able to win eventually. In 1955, Nizwa was taken, the imam had exiled to Saudi Arabia, but continued to lead the Imamate and guide the war efforts with a temporary government set-up in Dammam, Saudi Arabia. In 1959, the last forces of the Imamate were defeated and the name of the whole of Muscat and Oman was changed to the Sultanate of Oman in 1970. In current usage, "Oman proper" can also refer to the whole of the present-day sultanate minus the exclaves of Musandam and Madha.