This chapter provides a sense of the rupture that characterised the late nineteenth and early twentieth centuries by focusing on a series of political, technological and scholarly developments which contributed to creating a widespread atmosphere and experience of fundamental social change. I argue that crowds were seen as embodiments of these broader social transformations. Focusing on Gustave Le Bon’s crowd psychology, I discuss how theorisation on crowds was analytically indebted to late-nineteenth-century debates about hypnotic suggestion as these played out within psychotherapy. I argue that fin-de-siècle discussions of hypnotic suggestion did not simply propose that individuals are completely plastic creatures, always malleable in the hands of a powerful hypnotist. Rather, at the heart of the psychotherapy discussions at this time was the proposition that suggestion need not entail de-individualisation: the mimesis generated through suggestion may well depend on anti-mimetic individuals who must voluntarily let go of themselves in order for the mimetic suggestion to work. I discuss this in terms of tensional individuality.