Along with the rating of non-financial issuers, considered in previous Chapters (21–24), the rating of investment projects plays an important role in the modern economy and finance. It allows ranking and selection of the most effective investment projects, which is especially important for attracting both foreign and domestic investments. This Chapter discusses the rating of investment projects of arbitrary duration with a uniform repayment of debt, investment model for which is described in Chap. 16 . The methodology for rating investment projects has been modified. A fundamentally new approach to the project rating methodology has been developed, the key factors of which are: (1) adequate application of discounting when discounting the financial flows, which is practically not used in existing project rating methodologies; (2) incorporation of financial ratios into modern investment models created by the authors; (3) use rating parameters upon discounting; (4) the determination of the correct discount rate, taking into account financial ratios. We use modern investment model created by the authors (see Chap. 16 ), the modern theory of capital cost and capital structure by Brusov–Filatova–Orekhova (BFO theory), its modification for rating needs, and rating coefficients. Various theories of capital cost and capital structure are described in Chaps. 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , and 14 . The developed approach should be applied by rating agencies, both international and national ones, when rating investment projects. The modification of the methodology of the existing project rating systems will improve the accuracy of ratings of investment projects and make them more objective. The use of powerful tools of well-developed theories opens up new opportunities for the rating industry, which gets the opportunity to switch from using primarily qualitative methods for assessing the effectiveness of investment projects to using mainly quantitative methods for evaluating them.