Principles influence legislation, implementation and enforcement of the law to a great extent. This is especially the case with those fields of law, which are relatively new and subject to constant changes, such as environmental law. Principles have legal value, among others to fill legal gaps or to assist proper interpretation. It is always expedient to have a high-level judicial forum for legal interpretation at national level this would be a constitutional court or a supreme court. Legal interpretation can be particularly tricky when principles are combined with human rights. Constitutional courts, such as the Hungarian Constitutional Court are the preferred choice for such legal interpretation, since human rights are normally enshrined in the constitutions. In Hungary both the previous (1989) Constitution and the currently effective Fundamental Law of 2011 contain express and rather similar provisions regarding the right to environment, the content of which need clarification. Beside this similarity, the Fundamental Law has several other additional provisions supporting interpretation in the interests of the environment. This paper only presents – as examples of necessary interpretation – two principles to illustrate what the right to environment actually means. These are the non-regression (non-derogation) and the precautionary principles, which will be described both in general and in light of their current Hungarian interpretation. Non-regression (non-derogation) basically represents a decent minimum that should not be contravened, while precautionary principle is more in flux, a moving target, focusing on likely consequences, with scientific uncertainty at its core. Both principles will be introduced through the decisions of the Hungarian Constitutional Court.