The thesis is composed by three articles that are connected by the commom assumption of imperfections in the labor market. In the first article we study the relation between turnover of the labor force and investment in training when these decisions are taken in two periods and there is assimetric information about the type of the worker in the labor market. The main conclusion of the article is that not necessarily there is a trade-off between turnover and liquid investment in training, once although in an equilibrium with turnover the actual investment is reduced, if turnover is explained by the search for better matchings these must induce a greater level of training in the future. In the second article is considered an economy where worker`s ability is private knowledge and is discussed an arrangement of unemployment insurance that could induce more economic efficiency. The basic idea is to incorpotate in the unemployment insurance, originally a transfer instrument, an aspect of signaling, what can improve economic efficiency and can also reduce the cost for the government in providing this transfer. The third article studies the relation between wealth distribution and economic development. The contribution of the article is to match imperfection in the labor market (associated to the existence of an efficiency wage) and imperfection in the credit market in a model of occupational choice. The main conclusion is that into this context this imperfection in the labor market together with the perspective of high ascendent social mobility should conduce the economy to an state of prosperity, while were the labor market competitive an equilibrium of prosperity wouldn`t be reachead in cases when the inicial share of poor agents in the economy were high.