The purpose of this thesis is to examine, in the case of Greek firms of the Athens Stock Exchange (ASE), the information content of dividends in the unique Greek environment. In an effort to study the above mentioned issue an initial sample of 220 firms of the Athens Stock Exchange over the period 2002-2012 has been studied regarding the effect of dividend announcements on the firms’ stocks returns in the context of an event study. Results are presented based on three main categories of dividend announcements, above mandatory, mandatory and below mandatory dividend announcements for two periods 2002-2007 and 2008-2012. Furthermore results are also presented for the aforementioned periods regarding firms’ ownership structure, by examining the dividend announcement effect on stock returns in the case of firms exhibiting high ownership concentration by individuals. An introduction of the thesis is elaborated in the first part. The second part refers to a review of the existing literature regarding dividend policy, the agency problem, asymmetric information, signaling and event studies. The third part consists of an analysis of the data and the methodology used in the event study on the effect of the dividend payout announcements on the stocks returns. The results, based on the data and methodology, are included in the fourth part. Finally in the fifth part the conclusions of the thesis are presented.