The aim of this thesis is to examine the course of the development process of IFRS 16 - leases standard and the impact of the standard reform on the accounting treatment for leases. In addition the aim is to study how the Big Four entities have commented on the IFRS 16 standard reform at its various stages of development and how these entities react to the reform. The study has been conducted as a qualitative study. The empirical material of this study consists of the comment letters the Big Four entities have given regarding the discussion paper and two exposure drafts on the standard reform on accounting for leases published by the IASB and FASB. Based on the results of the research, the Big Four entities have, in principle, taken a positive view on the reforms introduced in IFRS 16. The aim of the reform to bring all leases into balance sheets are very welcome among the Big Four entities. In general, the Big Four entities agree with the proposed changes, but the views also show differences in detailed guidelines. In addition, the study shows the number of problematic issues that the Big Four entities disclose during the standard reform process.