The topic of the work is the harmonization of the purchase invoice process. The work was done for the client. The topic of the work was chosen according to the client’s needs. The aim was to make a comprehensive guide to the company’s purchase invoice process in an electronic financial management system. The aim of the guide was to harmonize the company's purchase invoicing process. The aim of harmonizing the purchase invoicing process is to speed up the process and reduce errors. The work was carried out as a functional thesis because the work is in two parts. In addition, the work provided a concrete guide for the company, which is not published due to confidential information in connection with the work. A table of contents and one example page were added to the guide as an appendix to the published part of the work. The work provided the client with an easy to read and comprehensive guide to the purchase invoice process of a harmonized company. In addition to the guide, a written report was made in the thesis. The written report tells the reader what was done at work, how it was done, and to whom it was done. The report provided information about the client, the method of carrying out the work, and work related concepts in the field. The correctness of the concepts was verified from the literature. When doing the thesis, one's own observation, literature, the Internet and especially blogs, articles and websites were used as information retrieval tools. My own observation took place while working as part of the purchase invoice process. In addition to the observation, information was sought by talking to people involved in the purchase invoicing process, and a kind of interview was conducted in addition to the discussion when I asked my predetermined questions to the case inspectors.