Pashtunistan (Pashto: پښتونستان, lit. 'land of the Pashtuns') or Pakhtunistan is a historical region on the crossroads of Central and South Asia, located on the Iranian Plateau, inhabited by the Pashtun people of southern and eastern Afghanistan and northwestern Pakistan, wherein Pashtun culture, the Pashto language, and identity have been based. Alternative names historically used for the region include Pashtūnkhwā or Pakhtūnkhwā (پښتونخوا), Pathānistān, or simply the Pashtun Belt.

During British rule in India in 1893, Mortimer Durand drew the Durand Line, fixing the limits of the spheres of influence between the Emirate of Afghanistan and British India during the Great Game and leaving about half of historical Pashtun territory under British colonial rule; after the partition of British India, the Durand Line now forms the internationally recognized border between Afghanistan and Pakistan. The traditional Pashtun homeland stretches roughly from the areas south of the Amu River in Afghanistan to the areas west of the Indus River in Pakistan; it predominantly comprises the southwestern, eastern and some northern and western districts of Afghanistan, as well as most of Khyber Pakhtunkhwa and northern Balochistan in Pakistan. The region is bordered by Punjab and Hazara to the east, Balochistan to the south, Kohistan and Chitral to the north, and Hazarajat and Tajik-inhabited territory to the west.

The 16th-century revolutionary Ormur leader Bayazid Pir Roshan of Waziristan and the 17th-century "warrior-poet" Khushal Khan Khattak assembled Pashtun armies to fight against the Mughal Empire in the region. During this time, the eastern parts of Pashtunistan were ruled by the Mughals while the western parts were ruled by Safavid Iran. Pashtunistan first gained an autonomous status in 1709, when Mirwais Hotak successfully revolted against the Safavids in Loy Kandahar. The Pashtuns later achieved unity under the leadership of Ahmad Shah Durrani, who founded the Durrani dynasty and established the Afghan Empire in 1747. In the 19th century, however, the Afghan Empire lost large parts of its eastern territory to the Sikh Empire and later the British Empire. Many famous Indian independence activists emerged from the region including Abdul Ghaffar Khan and his anti-colonial Khudai Khidmatgar movement to free the region from British control. In 1969, the autonomous princely states of Swat, Dir, Chitral, and Amb were merged into the Pakistani NWFP. In 2018, the Pashtun-majority Federally Administered Tribal Areas, formerly a federally-controlled buffer zone of Pakistan on the international border with Afghanistan, were merged into the province of Khyber Pakhtunkhwa (previously known as the NWFP), fully integrating the region with Pakistan proper.

The Pashtuns practice Pashtunwali, the indigenous culture of the Pashtuns, and this remains significant for many Pashtuns. Although the Pashtuns are politically separated by the Durand Line between Pakistan and Afghanistan, many Pashtun tribes from the FATA area and the adjacent regions of Afghanistan, tend to ignore the border and cross back and forth with relative ease to attend weddings, family functions and take part in the joint tribal councils known as jirgas. Depending on the source, the ethnic Pashtuns constitute 42-60% of the population of Afghanistan. In neighboring Pakistan they constitute 18 percent of over the 241 million population, which does not include Pashtun diaspora in other Pakistani cities and provinces.

The name used for the region during the Middle Ages especially during the High Middle Ages and Late Middle Ages and up until the 20th century was Afghanistan. Afghanistan is a reference to this land by its ethnicity, which were the Afghans, while Pashtunistan is a reference to this land by its language. Mention of this land by the name of Afghanistan predates mention by the name of Pashtunistan, which has been mentioned by Ahmad Shah Durrani in his famous couplet, 14th-century Moroccan scholar Ibn Battuta, Mughal Emperor Babur, 16th-century historian Firishta and many others. While mention of Afghans have been mentioned of a community of people, chieftains of tribes of Bactria known as Abgan or Avagana (Afğân) or Bactrian: αβγανο (Abgân) the exact origin or etymology of the term is not known with some scholars believe it to have been derived with the name Asvakan who were a people living in the Swat valley's then in the regions of Bactria.

The men of Kabul and Khilj also went home; and whenever they were questioned about the Musulmans of the Kohistan (the mountains), and how matters stood there, they said, "Don't call it Kohistan, but Afghanistan; for there is nothing there but Afghans and disturbances." Thus it is clear that for this reason the people of the country call their home in their own language Afghanistan, and themselves Afghans. But it occurs to me, that when, under the rule of Muhammadan sovereigns, Musulmans first came to the city of Patna, and dwelt there, the people of India (for that reason) called them Patans—but God knows!

— Firishta, 1560–1620

The Pashto name Pakhtunistan or Pashtunistan (Pashto: پښتونستان (Naskh)) evolved originally from the Indian word "Pathanistan" (Hindustani: پٹھانستان (Nastaleeq), पठानिस्तान (Devanagari)). The concept of Pashtunistan was inspired by the term "Pakhtunkhwa". British Indian leaders, including the Khudai Khidmatgar, started using the word "Pathanistan" to refer to the region, and later, the word "Pashtunistan" became more popular.