Democracy can take different forms and expressions among cultures and societies around the world, and, therefore, it can be characterised by different degrees. Accordingly, we asked how the degree of democracy affects economic growth. We choose the degree of political competitiveness among political parties as measure of the degree of democracy. We estimates cross-country panel data non-linear empirical growth model, taking into account the endogeneity of political competition through a new instrumental variable. The relationship between political competition and growth appears as an inverted U, and it is robust to the use of different political competition measures and to the short and long run analysis. This result allows us to calculate an 'optimal' level of political competition that maximises economic growth, which corresponds to a sufficient level of competition in the political vote market. We believe that this result emerges from the trade-offs generated by the various channels through which different levels of democracy (as those of political competition) affect growth. by presenting evidence of robust and sizable positive effects of democracy on economic growth.Democracy is more than just a set of specific government institutions. It rests upon a well-understood group of values, attitudes and practices, all of which may take different forms and expressions among cultures and societies around the world; democracies are based on fundamental principles, not uniform practices. This means that democratic countries over the world are characterised by different degrees of democracy. Therefore, the question to be asked is about the shape of the relationship between the degree of democracy and the level of economic growth. In other words, could this relationship be non-linear? This question arises from the analysis of a recent body of literature which supports a non-linearity of the effects of democracy on economic growth. Even in this branch of literature, two conflicting approaches to non-linearity emerge: the U-shape and the inverse U-shape of the effect of democracy on growth.In order to answer this important question, we need a measure for the level of democracy. We can find it by following the definition of democracy that the relevant literature proposes. According to Tavares and Wacziarg (2001, p. 1342), democracy is defined as 'a body of rules and procedure that regulates the transfer of political power and the free expression of disagreement at all levels of public life '. Schumpeter (1942) defines democracy as the political regime in which rulers are selected through free and contested elections; that is, democracy is a regime in which incumbents who lose elections must leave office. By these definitions, the right to form political parties and the freedom of political competition are the features that characterise better the level of democracy. Therefore, the degree of political competitiveness among political parties at elections appears to be an appropriate way of measuring the degree of democracy o...