Many libraries are currently facing challenges in obtaining sufficient financial support to continue and develop their services. Libraries around the world employed new strategies for overcoming this issue by adopting various revenue generation and marketing activities. This study is a systematized review conducted on revenue generation methods used in different types of libraries. To identify the relevant studies, two authors independently searched scholarly databases including Medline, Web of Science, Emerald, Science Direct, ERIC, ProQuest, Scopus, LISTA, PubMed Central, and Google Scholar search engine for published articles from 1995 to 2020. Articles were selected based on the inclusion and exclusion criteria. In total, 3461 articles were retrieved from which 56 were included for final analysis. This study identified 10 main categories with 75 sub-categories as different types of revenue generation methods suggested or used by various libraries around the world. Academic and public libraries were mostly reported in the reviewed articles as using different types of revenue generation. The most commonly used methods in libraries for revenue generation were public or governmental financial aid and receiving fees for providing services. The use of social networks, web space, and utilizing e-commerce principles were identified as the newest revenue-generating method, which were being implemented and developed in some public and academic libraries. Budget plays an important role in keeping library resources and services active and up to date. Therefore, discovering new opportunities for marketing and fundraising, as well as showing the value and return on investment of libraries is very important. Adopting and using methods introduced in this paper for revenue generation can help libraries to overcome some of their financial challenges well into the future.