In this paper, we discuss issues concerning the welfare of non-human primates used in laboratory research from an eco-ethological standpoint and suggest means of improving welfare. Following a brief review of the use of non-human primates in European countries and of the legislation that governs this use, we illustrate how a thorough eco-ethological knowledge of the species being studied can play a vital role in improving both its conditions and the quality of the experimental protocols, arguing that the animal's quality of life is closely linked to the quality of data. As a model for describing environmental enrichment techniques, we have used the common marmoset (Callithrix jacchus).