The wars of Alexander the Great (Greek: Πόλεμοι του Μεγάλου Αλεξάνδρου) were a series of conquests that were carried out by Alexander III of Macedon from 336 BC to 323 BC. They began with battles against the Achaemenid Persian Empire, then under the rule of Darius III of Persia. After Alexander's chain of victories against Achaemenid Persia, he began a campaign against local chieftains and warlords that stretched as far from Greece as the region of Punjab in South Asia. By the time of his death, he ruled over most regions of Greece and the conquered Achaemenid Empire (including much of Persian Egypt); he did not, however, manage to conquer the Indian subcontinent in its entirety as was his initial plan. Despite his military accomplishments, Alexander did not provide any stable alternative to the rule of the Achaemenid Empire, and his untimely death threw the vast territories he conquered into a series of civil wars, commonly known as the Wars of the Diadochi.

Alexander assumed kingship over ancient Macedonia following the assassination of his father, Philip II of Macedon (r. 359–336 BC). During his two decades on the throne, Philip II had unified the poleis (Greek city-states) of mainland Greece (with Macedonian hegemony) under the League of Corinth. Alexander proceeded to solidify Macedonian rule by quashing a rebellion that took place in the southern Greek city-states, and also staged a short but bloody excursion against the city-states to the north. He then proceeded east in order to carry out his plans to conquer the Achaemenid Empire. His campaign of conquests from Greece spanned across Anatolia, Syria, Phoenicia, Egypt, Mesopotamia, Persia, Afghanistan, and India. He extended the boundaries of his Macedonian Empire as far east as the city of Taxila in modern-day Pakistan.

Prior to his death, Alexander had also made plans for a Hellenic military and mercantile expansion into the Arabian Peninsula, after which he planned to turn his armies to Carthage, Rome, and the Iberian Peninsula in the west. However, the Diadochi (his political rivals) abandoned these plans after he died; instead, within a few years of Alexander's death, the Diadochi began a series of military campaigns against each other and divided the territories of the Macedonian Empire among themselves, triggering 40 years of warfare during the Hellenistic period.