Punjab (/pʌnˈdʒɑːb/ pun-JAHB; Punjabi, Urdu: پنجاب, pronounced [pəɲˈd͡ʒaːb] ^ⓘ) is a province of Pakistan. With a population of over 127 million, it is the most populous province in Pakistan and the second most populous subnational polity in the world. Located in the central-eastern region of the country, it has the largest economy, contributing the most to national GDP in Pakistan. Lahore is the capital and largest city of the province. Other major cities include Faisalabad, Rawalpindi, Gujranwala and Multan.

It is bordered by the Pakistani provinces of Khyber Pakhtunkhwa to the north-west, Balochistan to the south-west and Sindh to the south, as well as Islamabad Capital Territory to the north-west and Azad Kashmir to the north. It shares an international border with the Indian states of Rajasthan and Punjab to the east and Indian-administered Kashmir to the north-east. Punjab is the most fertile province of the country as the Indus River and its four major tributaries Ravi, Jhelum, Chenab, and Sutlej flow through it.

The province forms the bulk of the transnational Punjab region, partitioned in 1947 between Pakistan and India. The province is represented in the federal parliament through 173, out of 336, seats in National Assembly, the lower house; and 23, out of 96, seats in Senate, the upper house.

Punjab is Pakistan's most industrialised province, with the industrial sector comprising 24 per cent of the province's gross domestic product. It is known for its relative prosperity, and has the lowest rate of poverty among all Pakistani provinces. However, a clear divide is present between the northern and southern regions of the province; with northern Punjab being relatively more developed than southern Punjab. Punjab is also one of the most urbanised regions of South Asia, with approximately 40 percent of its population being concentrated in urban areas.

Punjabi Muslims form majority of the province. Their culture has been strongly influenced by Islamic culture and Sufism, with a number of Sufi shrines spread across the province. Guru Nanak, the founder of Sikhism, was born in the town of Nankana Sahib. Punjab hosts several of the UNESCO World Heritage Sites, including the Shalimar Gardens, the Lahore Fort, the archaeological excavations at Taxila, and the Rohtas Fort, among others.

The name "Punjab" consists of two parts (پنج, panj, 'five' and آب, āb, 'water'), of Persian origin which are cognates of the Sanskrit words (पञ्‍च, pañca, 'five' and अप्, áp, 'water'). The word pañj-āb is the calque of Indo-Aryan pañca-áp and means "The Land of Five Waters", referring to the rivers Jhelum, Chenab, Ravi, Sutlej, and Beas. All are tributaries of the Indus River, the Sutlej being the largest. References to a land of five rivers are found in the Mahabharata, in which one of the regions is named as Panchanada (Sanskrit: पञ्चनद, romanised: pañca-nada, lit. 'five rivers'). The ancient Greeks referred to the region as Pentapotamía (Greek: Πενταποταμία), of the same meaning as that of Punjab. Earlier, Punjab was also known as Sapta Sindhu in the Rigveda and Hapta Hendu in the Avesta, translating into "The Land of Seven Rivers"; the other two being Indus and Kabul which are included in the greater Punjab region. The current name gained currency during the Mughal period.

It is believed that the earliest evidence of human habitation in Punjab traces to the Soan Valley of the Pothohar, between the Indus and the Jhelum rivers, where Soanian culture developed between 774,000 BC and 11,700 BC. This period goes back to the first interglacial period in the second Ice Age, from which remnants of stone and flint tools have been found. The Punjab region was the site of one of the earliest cradle of civilisations, the Bronze Age Harrapan civilisation that flourished from about 3000 B.C. and declined rapidly 1,000 years later, following the Indo-Aryan migrations that overran the region in waves between 1500 and 500 B.C. The migrating Indo-Aryan tribes gave rise to the Iron Age Vedic civilisation, which lasted till 500 BC. During this era, the Rigveda was composed in Punjab, laying the foundation of Hinduism. Frequent intertribal wars in the post-Vedic period stimulated the growth of larger groupings ruled by chieftains and kings, who ruled local kingdoms known as Mahajanapadas. Achaemenid emperor Darius the Great, in 518 BCE crossed the Indus and annex the regions up to the Jhelum River. Taxila is considered to be the site of one of the oldest education centre of South Asia and was part of the Achaemenid province of Hindush.

One of the early kings in Punjab was Porus, who fought the famous Battle of the Hydaspes against Alexander the Great. The battle is thought to have resulted in a decisive Greek victory; however, A. B. Bosworth warns against an uncritical reading of Greek sources who were obviously exaggerative. Porus refused to surrender and wandered about atop an elephant, until he was wounded and his force routed. When asked by Alexander how he wished to be treated, Porus replied "Treat me as a king would treat another king". Despite the apparently one-sided results, Alexander was impressed by Porus and chose to not depose him. Not only was his territory reinstated but also expanded with Alexander's forces annexing the territories of Glausaes, who ruled to the northeast of Porus' kingdom. The battle is historically significant because it resulted in the syncretism of ancient Greek political and cultural influences on the Indian subcontinent, yielding works such as Greco-Buddhist art, which continued to have an impact for the ensuing centuries.