“The aim of this work is to show that there are different rationalities, different ways of being ‘right’, all of them legitimate though different, in the manner in which they account for the data of our senses”. This is how the author introduces his dissertation on the territories of reason, the subject of this volume. Henri Atlan, a doctor and biologist born in Algeria in 1931, currently teaches at the Universities of Paris and Jerusalem. He is the author of numerous studies on cell biology, biophysics and artificial intelligence. His formal theory of self-organisation has inspired fruitful intellectual explorations in various disciplines. In Italy he is known for his essay Tra il cristallo e il fumo, published by hopefulmonster in 1987.