The past two decades have resulted in an increase of international trade, capital flows and cross-border economic integrations. These phenomena have increased the demand for harmonized international accounting standards aimed to create an efficient resource allocation, worldwide. The adoption of IFRS is the result of a process towards a greater accounting harmonization. In Sweden, there are four categories of firms that apply IFRS; three are regulated by law, while the fourth are voluntary applying IFRS. The aim of this study is to find out which the factors are for the firms that voluntary apply IFRS and explain why they do it. We have found that there are 84 firms that voluntary apply IFRS, that is 35 percent. The significant factors to the voluntary application of IFRS are the use of an audit firm within the big four and the number of firms within the same industry that voluntary applies IFRS. Their voluntary application of IFRS has been explained to depend on the primarily advantages increased internal control, more extensive and detailed annual report, more investors, a good reputation in terms of a mark of quality and that the firms will be seen as good corporate citizen.