“Who Really Discovered the Electron?” is reprinted by permission from Jed Buchwald and Andrew Warwick, eds., Histories of the Electron: The Birth of MicroPhysics (MIT Press, 2001).

Written for a conference at MIT commemorating the 100th anniversary of the discovery of the electron. I provide a general account of what it means for someone to discover something and distinguish a weak and a strong sense of “discovery.” In terms of this account, I consider historically whether J. J. Thomson, who is generally regarded as the discoverer of the electron, deserves that title.