This paper estimates the size of the shadow economy in 110 countries, including developing, transition, and developed OECD countries, using the DYMIMIC approach. The average size of the shadow economy (as a percentage of official GDP) is 41% in developing countries, 38% in transition countries, and 17% in OECD countries. The shadow economy is driven by high tax and social security contribution burdens, as well as strict regulations. The paper finds that an increase in the shadow economy by 1% reduces the growth rate of the official GDP of a developing country by 0.6%, while increasing it by 0.8% and 1.0% for developed and transition countries, respectively. The study also shows that the shadow economy has dynamic effects on the official economy, with a negative impact on growth in developing countries and a positive impact in developed countries. The results indicate that the shadow economy is a significant factor in economic growth, with different effects depending on the country's development level. The paper concludes that the shadow economy is a complex phenomenon influenced by various factors, and that further research is needed to fully understand its impact on economic growth.This paper estimates the size of the shadow economy in 110 countries, including developing, transition, and developed OECD countries, using the DYMIMIC approach. The average size of the shadow economy (as a percentage of official GDP) is 41% in developing countries, 38% in transition countries, and 17% in OECD countries. The shadow economy is driven by high tax and social security contribution burdens, as well as strict regulations. The paper finds that an increase in the shadow economy by 1% reduces the growth rate of the official GDP of a developing country by 0.6%, while increasing it by 0.8% and 1.0% for developed and transition countries, respectively. The study also shows that the shadow economy has dynamic effects on the official economy, with a negative impact on growth in developing countries and a positive impact in developed countries. The results indicate that the shadow economy is a significant factor in economic growth, with different effects depending on the country's development level. The paper concludes that the shadow economy is a complex phenomenon influenced by various factors, and that further research is needed to fully understand its impact on economic growth.