The aim of this thesis is to increase our understanding of the processes underlying public acceptance of novel (energy) technologies. Especially when people know little about an issue, which typically is the case with new technologies, subtle differences in the way the issue is introduced may influence their attitudes. In seven experiments the boundary conditions for the occurrence of context effects were investigated, as well as the processes underlying these effects. The focal topic was the use of biomass for electricity generation. The results show that people only are sensitive to context effects when their prior attitudes towards biomass are weak. When attitudes were weak and another energy source was mentioned casually just before people were asked to evaluate biomass, they assimilated their judgment towards this other energy source. They evaluated biomass more positively following solar energy than following coal. Under specific circumstances however, the opposite effect was found. When the context object was made distinct by having people evaluate it explicitly before evaluating the target object, contrast occurred. Judgments about biomass then turned out to be more negative when made in the context of solar energy, than when made in the context of coal. Contrast was found to only occur in the case of unlimited cognitive capacity. In addition, contrast appeared to be dimension specific. Assimilation, on the other hand, was found to occur regardless of cognitive capacity and issue involvement. The results are in line with the theory that assimilation is due to the use of a contextual object as an interpretation frame, to make sense of an unfamiliar target object. On the other hand, contrast occurs when the contextual object is used as a standard with which the target object is compared. The findings substantiate the notion that contrary to the interpretation process, the comparison process is effortful. The alternative explanation that context effects would be due to a simple correction process is challenged by the results. People will often form attitudes towards new technologies based on limited information, due to the complexity of the issue, a lack of involvement, or time limitations. The research provides reasons to assume that people’s attitudes towards novel energy sources are related to each other. Communication about one energy source can influence the evaluation of another, novel, energy source. For instance the contextual presence of a positively evaluated energy source may result in more positive attitudes towards a novel object. Alternatively, the contextual presence of a positively evaluated energy source may also result in the opposite effect. As a result of comparison with a positively evaluated energy source, biomass may be more negatively evaluated. This implies that promotion of one energy source can reduce the acceptance of other (novel) energy sources. Given that multiple energy sources have been introduced in the Netherlands and are communicated about, this research stresses the importance of an integrated communication strategy for the acceptance of all these energy sources. The research presented in this dissertation sheds more light on the processes underlying attitude formation under these circumstances and on the subtle influences of the contextual embeddedness of technologies.