This thesis sheds light on several macroeconomic aspects of labor markets. The first chapter focuses on the impact of dual labor markets on human capital investment. Using a large dataset of the Spanish Social Security the wage losses of permanent and fixed term workers after displacement are analyzed. Results indicate that workers under permanent contracts accumulate a higher share of firm specific human capital than workers under fixed term contracts. The impact on aggregate productivity is analyzed using a calibrated model à la Mortensen and Pissarides (1994) with endogenous investment in human capital and dual labor markets. The second chapter develops a model in order to explain cross countries differences in the cyclical fluctuations of informal employment for developing countries. The explanation can be found in institutional differences between the formal and informal sector. The third chapter proposes a model that uses the flows into and out of unemployment to forecast the unemployment rate. It shows why this model should outperform standard time series models, and quantifies empirically this contribution for several OECD countries.