This thesis explores the ECINF database, a survey conducted by the Brazilian Census Bureau that investigates micro- enterprises in Brazil, in two different aspects. First, the enactment of a new tax registration system (SIMPLES) is investigated. This system has reduced the tax collection of small and micro enterprises in Brazil. Using difference in difference and propensity score matching methods, it was found that the new system has increased the formality among firms in the retail sector. Second, the linked employer-employee nature of the data was used to study the issue of matching between employers and employees. The results indicate the presence of matching in the labor contracts. There is evidence that employers tend to contract workers with the same gender, age and educational level. Moreover, it is shown that this matching affects the contract form. People with the same gender and educational level prefer piece rate contracts.