Under Ptolemy I Soter and his son Ptolemy II Philadelphus, Alexandria — Egypt's new capital after Alexander's death — became the most ambitious cultural project of its time. At the palace's center the Mouseion (Shrine of the Muses) was a research complex: an observation terrace, an anatomy hall, botanical gardens, and a refectory, with a great Library attached. Foundation dates are not exact; the nucleus was laid under Ptolemy I (around 300 BCE) and the institution matured under Ptolemy II (the 280s).

The Library pursued a systematic acquisition policy — manuscripts from every ship docking at the harbor were copied — and competed with Athens and Pergamon. Ancient sources give holdings of 400,000–700,000 scrolls at its peak; the figures include exaggeration but the unprecedented scale is generally accepted. Scholars who worked there or were closely tied to it include Euclid (geometry), Eratosthenes (who calculated the Earth's circumference), Aristarchus (an early heliocentric proposal), Archimedes (known to have visited), and Herophilus (a forerunner of Galen in human anatomy). The first systematic philological editions of Homer were also produced there.

It is misleading to date the Library's end to a single fire. Caesar's fire of 48 BCE inflicted serious damage; in the following centuries — the destruction of the Brucheion under Aurelian (270s CE), late-antique religious and political conflicts, the drying up of state funding — the institution eroded. The Library disappeared not in a day but across a three-century decline. Its true legacy is not the book collection but the model of state-supported, organized research; the modern university and research institute are its distant descendants.