This paper shows the most widespread and accepted capital structure theories in the finance world form the fifties until today. In a chronological order, it identifies the best known research work and its authors, the factors analized, the hypothesis, the scenarios and the economic theories supporting them. It also presents the most controversial aspects. The thesis are compared, and the relationship between leverage, capital cost and firm valuation is analized. This paper provides an overview of the state of art capital structure in corporations today.