The underground economy is part of the economic sciences, being a component that should not be neglected in the economic analysis, with a stronger impact on economic indicators, and is an unavoidable ingredient of a country's economy, in most cases the most profitable part of an economy being the underground one.
The purpose of this paper is to define the underground economy and, implicitly, to identify the main causes, the methods of its detection and evaluation, as well as to achieve a comparative situation regarding the size of the underground economy in Moldova and some EU Member States and, subsequently, to propose solutions to diminish its value We will use a descriptive methodology, consisting of collecting data and information from the specialized literature and practice.