Energy reduction has been on the political agenda since the last couple of decades. One of the most common policies to reduce energy consumption has been improving efficiency. However, the phenomenon called the rebound effect may threaten the effectiveness of policies aiming to reduce consumption by improving efficiency. The rebound effect is the process in which energy savings, after energy efficiency improvements, are lower than expected. The scientific community agrees on the existence of the rebound effect and the possibility to measure it. In spite of this agreement, the rebound effect has been catalogued by many scholars as a highly controversial concept. In fact, the two main controversies around the rebound effect are: its size and its importance for the policy making process. The main causes that have produced the rebound effect to be controversial are: methodological issues of previous attempts to assess the effect, different numeric definitions and fuzzy and different system boundaries. The main objective of this thesis research was to find a new and innovative methodology to assess the rebound effect in order to improve the methodological issues of previous attempts that have analyzed the rebound effect. As a result, in reducing the causes of controversies, the controversies themselves may be reduced as well. The methodology that seems to improve the mentioned methodological issues is serious games. Serious games have several advantages that seem to fit and solve the shortcomings of the previous attempts that have analyzed the rebound effect in the past. In particular, the NRG game is the specific serious game that was used to perform the actual assessment in this research. The NRG game was used to carry out a new rebound effect assessment. In doing so, 50 people played the game in two different groups in a way to perform a modified before/after analysis: one group of 25 people using a low efficiency house and 25 people using a high efficiency house. The conclusions of this assessment showed that the rebound effect was, indeed, detected to be present when the behavior of the two groups was compared. In fact, two main signs of the rebound effect were detected. First, having a low efficiency made the low efficiency group to reduce their energy consumption more than the high efficiency group. Second, having a high efficiency made the high efficiency group to increase their comfort level (a direct measure of the luxury level of their houses in the game) more than the low efficiency group. As a result, the rebound effect was detected by keeping track of the total energy consumption and comfort level of each player. In addition, some of the methodological issues of previous rebound effect assessments that have used before/after analysis were improved, for instance, the possibility to perform ex-ante assessments, the inclusion of psychological factors of people in the results without making inaccurate assumptions and the inclusion of more than just one energy services in the experiments, among others. As a result, serious games were proven to be a handy tool to assess and analyze the rebound effect, improving the quality of previous assessments. Despite having proved the usefulness of serious games in assessing the rebound effect, some limitations of this research were identified: the sample under study was not a good representation of the population, the reliability of the rebound effect size calculation is compromised, the findings of this assessment can’t be applied in a real life context and so forth.