Recently, there has been growing interest in the use of Serious Games (SG), as they provide a more powerful means of knowledge transfer in almost every application domain especially in the crisis management field. With this increasing adoption of SG, designing novel techniques for learners' assessment and evaluation has become of paramount importance to improve learning results and thus to maintain players' motivation. This paper focuses on the learners' assessment and evaluation in SG. After defining assessment and evaluation, we distinguish two main approaches: implicit and explicit. For each of these approaches, we present some techniques currently used in some existing games. Then we compare these different approaches and techniques. This synthesis is expected to help researchers and games creators working in this area and identifying benefits and limitations of these techniques in order to develop a new comprehensive technique that outperforms all existing ones.