The meeting of Diogenes of Sinope and Alexander the Great is one of the most discussed anecdotes from philosophical history. Many versions of it exist. The most popular relate it as evidence of Diogenes' disregard for authority, wealth, and decorum.

Plutarch and Diogenes Laërtius report that Alexander and Diogenes died on the same day, in 323 BC. Although this account is dubious (since neither man's date of death can be conclusively verified), the anecdote, and the relationship between the two people, has been the subject of many literary and artistic works over the centuries, from the writings of Diogenes Laërtius to David Pinski's 1930 dramatic reconstruction of the encounter, Aleḳsander un Dyogenes; including writings from the Middle Ages, several works of Henry Fielding, and possibly even Shakespeare's King Lear along the way. The literature and artwork influenced by this story are extensive.

Versions upon versions of the anecdote exist, with the origins of most appearing to be, either directly or indirectly, in the account of the meeting given by Plutarch, whose actual historicity has also been questioned. Several of the embellished versions of the anecdote do not name either one or both of the protagonists, and some indeed substitute Socrates for Diogenes.

According to legend, Alexander the Great came to visit the philosopher Diogenes of Sinope. Alexander wanted to fulfill a wish for Diogenes and asked him what he desired. As told by Diogenes Laërtius, Diogenes replied, "Stand out of my light." Plutarch provides a longer version of the story, which begins after Alexander arrives in Corinth:

Thereupon many statesmen and philosophers came to Alexander with their congratulations, and he expected that Diogenes of Sinope also, who was tarrying in Corinth, would do likewise. But since that philosopher took not the slightest notice of Alexander, and continued to enjoy his leisure in the suburb Craneion, Alexander went in person to see him, and he found him lying in the sun. Diogenes raised himself up a little when he saw so many people coming towards him, and fixed his eyes upon Alexander. And when that monarch addressed him with greetings, and asked if he wanted anything, "Yes," said Diogenes, "stand a little out of my sun." It is said that Alexander was so struck by this, and admired so much the haughtiness and grandeur of the man who had nothing but scorn for him, that he said to his followers, who were laughing and jesting about the philosopher as they went away, "But truly, if I were not Alexander, I wish I were Diogenes."

There are many minor variants of what Diogenes is supposed to have replied to Alexander. According to Cicero, Diogenes answered Alexander with the words, "Now move at least a little out of the sun". According to Valerius Maximus, Diogenes answered: "To this later, for now I just want you not to stand in the sun." The statement by Alexander, "if I were not Alexander the Great, I would like to be Diogenes," also crops up in some other versions of the anecdote.

Arrian referred to the episode when recording the similar encounters of Indian philosophers with Alexander occurred during Alexander's campaigns in his book The Campaigns of Alexander.

When also in the Isthmus he met Diogenes of Sinope, lying in the sun, standing near him with his shield-bearing guards and foot Companions, he asked if he wanted anything. But Diogenes said that he wanted nothing else, except that he and his attendants would stand out of the sun. Alexander is said to have expressed his admiration of Diogenes's conduct. Thus it is evident that Alexander was not entirely destitute of better feelings; but he was the slave of his insatiable ambition.