Individuals such as René Descartes, Rembrandt, Christiaan Huygens, Hugo Grotius, Benedictus Spinoza, and later Baron d'Holbach were active in Leiden and environs.

The university has seven academic faculties and over fifty subject departments, housing more than forty national and international research institutes.

The name of Philip II of Spain, William's adversary, appears on the official foundation certificate as he was still the de jure count of Holland.

[12] Leiden University's reputation was created in part by the presence of scholars such as Justus Lipsius, Joseph Scaliger, Franciscus Gomarus, Hugo Grotius, Jacobus Arminius, Daniel Heinsius, and Gerhard Johann Vossius within fifty years of its founding.

[15][13] Baruch Spinoza discovered Descartes's work partly at Leiden University,[16] which he visited for periods of study multiple times.

[17] In the 18th century, Jacobus Gronovius, Herman Boerhaave, Tiberius Hemsterhuis, and David Ruhnken were among the renowned academics of the university.

[18] In the world's first university low-temperature laboratory, Professor Heike Kamerlingh Onnes achieved a temperature only one degree above absolute zero.

In 2005, the manuscript of Einstein on the quantum theory of the monatomic ideal gas (the Einstein-Bose condensation) was discovered in one of Leiden's libraries.

The university is also the unofficial home of the Bilderberg Group, a meeting of high-level political and economic figures from North America and Europe.

The MPhil is the most advanced graduate degree and is awarded by select university departments (mostly in the fields of Arts, Social Sciences, Archeology, Philosophy, and Theology).

Of the 107 Spinoza Prize laureates (the highest scientific award of The Netherlands), twenty-six were granted to professors of Leiden University.

Other Spinoza Prize winners are linguists Frederik Kortlandt and Pieter Muysken, mathematician Hendrik Lenstra, physicists Carlo Beenakker, Jan Zaanen, Dirk Bouwmeester and Michel Orrit, astronomers Ewine van Dishoeck, Marijn Franx and Alexander Tielens, transplantation biologist Els Goulmy, clinical epidemiologist Frits Rosendaal, pedagogue Marinus van IJzendoorn, archeologists Wil Roebroeks and Corinne Hofman, neurologist Michel Ferrari, classicist Ineke Sluiter, social psychologist Naomi Ellemers, statistician Aad van der Vaart, cognitive psychologist Eveline Crone, organisation psychologist Carsten de Dreu, chemical immunologist Sjaak Neefjes, parasitologist Maria Yazdanbakhsh, electrochemist Mark Koper and astrophysicist Ignas Snellen.

Three other professors received the Nobel Prize for their research performed at Universiteit Leiden: Hendrik Antoon Lorentz and Pieter Zeeman received the Nobel Prize for their pioneering work in the field of optical and electronic phenomena, and the physiologist Willem Einthoven for his invention of the string galvanometer, which among other things, enabled the development of electrocardiography.

Nobel laureates associated with Leiden include the physicists Albert Einstein, Enrico Fermi, and Paul Ehrenfest.