The paper presents major findings from the multi-year study of informality in the Russian labor market conducted by the CLMS—HSE. The authors argue that the concept of informality though it seems to be intuitively clear is neither conceptually straightforward, nor easily measurable, nor univocal in terms of economic and social implications. The article explores the issues related to definitions, measurement, evolution, profiling, impact of institutions, mobility, earnings and inequality. All findings and conclusions are supported by special econometric studies and large data sets.