The Battle of the Hydaspes River was fought by Alexander the Great in 326 BC against King Porus of the Hindu Paurava kingdom on the banks of the Hydaspes River (Jhelum River) in the Punjab near Bhera in what is now modern-day Pakistan. The battle resulted in a complete Macedonian victory and the annexation of the Punjab, which lay beyond the confines of the defeated Persian empire, into the Alexandrian Empire.

Alexander's tactics to cross the monsoon-swollen river despite close Indian surveillance to catch Porus' army in the flank has been referred as one of his "masterpieces". Although victorious, it was also the most costly battle fought by the Macedonians. The resistance put up by King Porus and his men won the respect of Alexander who asked him to become a Macedonian satrap.

The battle is historically significant for opening up India for Greek political (Seleucid Empire, Indo-Greeks) and cultural influence (Greco-Buddhist art) which was to continue for many centuries.

The battle took place on the east bank of the Hydaspes River (now called the river Jhelum, a tributary of the river Indus) in what is now the Punjab province of Pakistan. Later, Alexander founded a city on the site of the battle, which he called Nicaea; as long as this city has not been discovered, any attempt to find the ancient battle site is doomed, because the landscape has changed considerably. For the moment, the most plausible location is just south of the city of Jhelum, where the ancient main road crossed the river, and where a Buddhist source indeed mentions a city that may be Nicaea. The identification of the battle site near modern Jalalpur/Haranpur is certainly erroneous, as the river, in the ancient times, meandered far from these cities.

Alexander III of Macedon (20/21 July 356 – 10/11 June 323 BC), commonly known as Alexander the Great (Greek: Ἀλέξανδρος ὁ Μέγας, Aléxandros ho Mégas from the Greek αλέξω alexo "to defend, help" + ανήρ aner "man"), was a king of Macedon, a state in northern ancient Greece. Born in Pella in 356 BC, Alexander was tutored by Aristotle until the age of 16. By the age of thirty, he had created one of the largest empires of the ancient world, stretching from the Ionian Sea to the Himalayas. He was undefeated in battle and is considered one of history's most successful commanders.

Alexander succeeded his father, Philip II of Macedon, to the throne in 336 BC after Philip was assassinated. Upon Philip's death, Alexander inherited a strong kingdom and an experienced army. He was awarded the generalship of Greece and used this authority to launch his father's military expansion plans. In 334 BC, he invaded Persian-ruled Asia Minor and began a series of campaigns that lasted ten years. Alexander broke the power of Persia in a series of decisive battles, most notably the battles of Issus and Gaugamela. He subsequently overthrew the Persian King Darius III and conquered the entirety of the Persian Empire. At that point, his empire stretched from the Adriatic Sea to the Indus River.