||Interactive navigable 3D visualisations of built and natural environments have become commonplace in design and planning of urban environments and landscapes, and are regarded as potent prototyping and communication tools. In training applications, for instance for fire fighters, virtual environments displayed on desktop monitors or on projection screens are used to represent situations and scenarios that cannot be created in the real world for reasons of safety, cost, and time. A valid simulated environment should induce not only a cognitive, but also an emotional response in the observer equivalent to the response to the real environment. For visualisations, this means that viewers experience the ‘ambience’ of a place as they would in the real environment. In training environments and serious games, the emotional response of the trainee to the virtual scenario should be similar to the response in a real, often stressful, situation. A common assumption is that the highest possible level of photorealism ensures a valid representation. However, the focus in the development of virtual environments is on spatial tasks or other cognitive tasks, not on the affective qualities of an environment. The virtual environments do not contain the required information for that purpose, which can be visual, but also of other sensory modalities (audio, tactile and olfactory). In eight empirical studies (lab experiments and field studies) we examined factors in the content and representation of the virtual environment, and factors related to user characteristics, and their effects on the emotional response of users. We found that when users appraise a virtual environment they do not distinguish between their appraisals of the represented environment, of the representation, and of their pre-existing individual mental representations. The mental representation fills in more information than the user is aware of. The user’s emotional state, induced by other factors than the virtual environment, such as cybersickness, may influence the appraisal of the virtual environment. The absence of personal involvement, factors that diminish the perceived (graphics and audio) quality of the 3D environment, and factors that distract the attention of the user, attenuate the impact of cues and thereby the intensity of the emotional response. The importance of personal involvement and the context of use of a visualisation or a virtual training for their validity are generally underestimated. We discern three categories of features of real environments, relating to spatial layout and functionality, to the meaning and function of elements of the environment, and ambient conditions, that can be used to guide the modeling process. We developed a comprehensive framework containing factors (such as features of the environment, representational modifiers and response moderators) that influence and modify the appraisal process in virtual environments, that can be used for measuring emotional responses in virtual environments. We complete our research with guidelines for the development and use of desktop virtual environments for visualisations and training applications.