In the matter of corporate governance reforms, an important aspect is whether the implementation of corporate governance principles and codes has a positive impact on firm performance. The literature testing the relationship between different corporate governance mechanisms and firm performance is extensive. Over time, a lot of corporate governances mechanisms were studied in relation to firm performance and the most used are: CEO duality, board size, proportion of non- executive directors, board committees, ownership structure and concentration, managers’ compensation and incentives schemes. With time, different authors began to use more comprehensive measures for corporate governance rather than a single variable or a single governance mechanism, the so called corporate governance indexes. Regarding performance there are three main approaches to firm performance in social science research: research based on market prices, accounting ratios and total factor profitability.The most used performance measures are: Tobin’s Q, return on equity, return on asset and economic value added. In our paper, we present the studies undertaken since the 1990’s regarding the relationship between different mechanisms of corporate governance and firm performance and between corporate governance index and performance for both developed and developing countries around the world. Regarding the working tools used in this theoretical research we can mention the longitudinal method, by presenting the evolution in time of empirical studies on the research topic and the comparative method used in presenting the resulys of different studies mentioned in our paper. The results of the studies are inconclusive, some studies founded a strog positive relation, others founded a negative correlation between corporate governance and firm performance, while a third category of studies didn’t found any relationship at all. We used participative observation method by issuing conclusions on the potential causes of the inconclusive results on the existence and nature of the relationship between corporate governance and firm performance.