Digital natives demand a more active approach to learning. Moreover, the acquisition and assessment of competencies, rather than the mere transmission of information, is becoming more relevant in the Knowledge Society. 3D virtual worlds are a promising environment to meet both of these requirements. In a 3D virtual world, learners are immersed in a rich environment that allows them to have an active experience through their avatars and interaction devices. The learning process in traditional learning management systems has been widely studied, but there is relatively little literature about the use of 3D virtual worlds for learning, although the expectations are high and the possibilities opened immense. This paper focuses on an important part of the teaching and learning process: the assessment. Our aim is to present a set of techniques adapted to this novel 3D medium that allows assessing knowledge, skills, and competencies by using the elements inherent to 3D virtual worlds (avatars, synthetic characters, smart objects) and take advantage of the new dimension introduced.