At the beginning of the 20th century, German biologist Jakob von UexkA1/4ll created the concept of "Umwelt" to denote the environment as experienced by a subject. This concept of environment differs from the idea of passive surroundings and is defined not just by physical surroundings, but is rather a "subjective universe," a space weighted with meaning. Today, neuroscience provides a new way to look at the braina (TM)s capability to create a representation of the world. At the same time behavioural specialists are demonstrating that animals have a richer mental universe than previously known. Philosophical reflection thus finds itself with more experimental and objective data as well. Nearly a century after the publication of von UexkA1/4lla (TM)s founding work ("Umwelt und Innenwelt der Tiere" was published in 1909), neurobiologists, psychologists, sociologists, anthropologists, ethologists, and philosophers revisit his mail concept at the light of modern science