This paper discusses current state-of-the-art features of the “plant evaluation model”, a framework which, starting from the representation of vegetation and its effects in microclimate models, defines a number of indices which can be employed for the evaluation of outdoor microclimate in terms of thermal environment and comfort in the urban environment. The key point of taking into account the impact of vegetation on microclimate is to implement appropriate parameterizations of such impact in a microclimate model. The paper, based on a review of literature studies, thus illustrates the basic principle and technical path of the impact assessment model of vegetation on microclimate and introduces related software. The aim is to provide the scientific community with a summary of (i) the current definition of vegetation in models employed for the evaluation of the impact of vegetation on urban outdoor microclimate, (ii) main models and evaluation indices and (iii) main input, output, vegetation-related processes implemented, strengths and weaknesses of those models, with suggested measures for output improvement. This review is not exhaustive but may help the user to select the proper model, which takes into account the effects of vegetation on outdoor urban microclimate, depending on the specific objective.