Abstract: I develop a labor market framework when monopsony power, informality and self-employment are simultaneously present - a salient characteristic of developing economies’ labor markets. I construct a model of heterogeneous firms with endogenous entry and calibrate it with Brazilian data. Firms self-select into formality or informality andworkers have the outside option of working as self-employed. From the firm’s per-spective, labor supply elasticity is endogenously determined by competition between formal and informal firms, across sectors and against self-employment. I find that while monopsony power is responsible for significant welfare losses, to the order of 5%, firm informality can be welfare improving, albeit only slightly. Finally, shifting the fiscal burden from marginal taxation (such as payroll taxes) to corporate taxation massively improves labor allocation, firm entry and welfare