The study of legal documents framing the working of the guilds enabled the author to describe the workshops of painters active in the Southern Netherlands between about 1400 and 1530, and to analyze the many levels of collaboration among masters (dealing in art, subcontracting work, commissioning pictures), and masters and assistants (apprentices, <i>compagnons</i>, visiting artists, etc.). Apprenticeship and <i>compagnonnage</i> are studied in detail and contrasted. The stylistic influence of masters, the great and necessary adaptability of assitants are further factors that contribute to the complexity of the problem of attribution in art. Indeed, many 15th-century paintings may have been the product of highly organized collaboration. -- AATA