This thesis studies the influence of credit officer in the mechanisms of microcredit based on a database from Vivacred, an NGO operating in Rio de Janeiro s slums. A brief history of Vivacred and microcredit in Brazil is presented in chapter two. Chapter three estimates a structural model and show credit officer s ability is more heterogeneous in selection that audit phase. Furthermore, officer s ability is correlated with the internal experience, but not with the previous one, showing the importance of human resource management. As credit officers have a relative autonomy, the remaining chapters analyze whether this translates into discriminatory behavior toward women. The fourth chapter documents that women enjoy equal access to credit, but obtain lower volumes than men. The offcer (respectively the credit committee) is responsible for 27.3 percent (resp. 7.4 percent) of the difference in loan size between genders, while 65.3 percent is attributable to the women themselves as they request significantly lower amounts. The fifth chapter compares genders in terms of delay, default and loss. For the same loan size, women repay better than men, in the three dimensions, implying that the difference found in the previous chapter is not economically justified. Moreover, the gender-gap is not reduced along the relationship, as it would be expected if its origin was asymmetric information. A theoretical model à la Becker, the sixth chapter, shows that discrimination can lead to three possible situations: the rejection of female applicants, loan downsizing for female or no impact. Empirical results confirm the second case. We tend to attribute these results to cultural habits. Women lack credibility, especially among the most ambitious ones. We do not believe that this phenomenon is necessarily conscious or volunteer. This work simply aims at contibuting to a re exion on fair attendance.