This work, by Professor Bergson, has been revised in detail by the author himself, and the present translation is the only authorised one. For this ungrudging labour of revision, for the thoroughness with which it has been carried out, and for personal sympathy in many a difficulty of word and phrase, we desire to offer our grateful acknowledgment to Professor Bergson. It may be pointed out that the essay on Laughter originally appeared in a series of three articles in one of the leading magazines in France, the Revue de Paris