Jalalabad, previously known as Tarunshahr, and historically known as Nagarahara or Adinapur, is the fifth-largest city of Afghanistan. It has a population of about 200,331, and serves as the capital of Nangarhar Province in the eastern part of the country, about 130 kilometres (80 mi) from the capital Kabul. Jalalabad is located at the junction of the Kabul River and the Kunar River in a plateau to the south of the Hindu Kush mountains. It is linked by the Kabul-Jalalabad Road to the west and Peshawar in Khyber Pakhtunkhwa, Pakistan, to the east through Torkham and the Khyber Pass.

Jalalabad is a leading center of social and trade activity because of its proximity with the Torkham border checkpoint and border crossing, 65 km (40 mi) away. Major industries include papermaking, as well as agricultural products including oranges, lemon, rice, and sugarcane, helped by its warm climate. It hosts Afghanistan's second largest educational institute, Nangarhar University. For centuries the city was favored by Afghan kings and it has a cultural significance in Afghan poetry. During Timur Shah's reign of the Durrani Empire, Jalalabad served as the Afghan winter capital.

Known at the time by names such as Nagarahara and Adinapur, Jalalabad was a major center of Greco-Buddhist culture during the late 1st millennium BCE, focused on sites such as Ahin Posh.

The first surviving references to the city are in early 1st millennium CE accounts by visiting Chinese Buddhist monks. In or about 400 CE, Faxian visited "Nagarahara" and worshiped at sacred Buddhist sites, such as the "Cave of the Buddha's Shadow” (佛影窟). In 630 CE, Xuan Zang, visited "Adinapur" and other locations nearby.

The Buddhist era began to end after the region was conquered by Muslim forces during the late 1st Millennium. However, conversions to Islam evidently did not occur quickly. In Hudud-al-Alam, written in 982 CE, there is reference to a village near Jalalabad where the local king had Muslim, Buddhist and Hindu wives.

The region became part of the Ghaznavid Empire in the 10th century. Sabuktigin annexed the land all the way west of the Neelum River in Kashmir. "The Afghans and Khiljies who resided among the mountains having taken the oath of allegiance to Sabuktigin, many of them were enlisted in his army, after which he returned in triumph to Ghazni." The Ghurids succeeded the Ghaznavids and expanded the Islamic empire further into Hindustan. The region around Jalalabad later became part of the Khalji territory, followed by that of the Timurids.

It is said that the original name of Jalalabad was Adinapur or Nagar(a)hara. Jalalabad was named in the last decade of the sixteenth century in honour of Mughal ruler Jalal-uddin Mohammad Akbar, the grandson of the founder of the Mughal Empire: Babur. Babur had chosen the site for this city which was built by his grandson in 1560.

It remained part of the Mughal Empire until around 1738 when Nader Shah and his Afsharid forces defeated the Mughals. Nader Shah's forces were accompanied by the young Ahmad Shah Durrani and his 4,000-strong Afghan army from southern Afghanistan. In 1747, he founded the Durrani Empire (Afghan Empire) after re-conquering the area. The Afghan army has long used the city while going back and forth during their military campaigns into the Indian-subcontinent.