The underground economy or black market is a market consisting of all economic affairs, commerce on which applicable taxes and/or regulations of economic and trade are being avoided. The term is also known as the underdog, shadow, black economy. The main aim of the article is to investigate the principles, the structure of the shadow economy in the Republic of Moldova and the forms of its manifestation. The actuality of subject of investigation has been grounded because it becomes progressively, increased. The authors try to investigate the principles of the shadow economy its kinds, the causes of its appearance, the scale of underground economy in the Republic of Moldova and struggle with it.