For a decade or so environmental impact assessments have been a tool used in an investment process in order to evaluate an impact of a planning document or a given construction project on the environment. The legal regulation in force approach selectively to determine elements making up each assessment. There is also a lack of methodological guidelines pertaining to the rules of assessment making (such guidelines were prepared in reference of e.g. motorways or wind power plants). It makes it difficult to understand the aims and the range of environmental impact assessments by society and investors as well as obtaining acceptance for making them by the latter. The article presents the issue of the principal environmental assessments (strategic environmental impact assessment, environmental impact assessment and impact assessment on Natura 2000 sites) in the legal and methodological context. The researchers done showed that unstable legal system in the field of environmental assessments endangers correctness and punctuality of preparation of an building investment.