The paper analyzes similarities and differences between fair use and fair dealing doctrines in copyright law that allow for limited use of copyright-protected material without the need of permission from the rightholder. Both concepts have long been part of legislation but have recently gained special interest due to the wide spread of digital technologies and the ease of copying materials, both text ones and any other digitized materials. What kind of use may be deemed fair and what may not, has become the question of everyday interest. Copyright exceptions implemented in the form of fair use or fair dealing concepts are of special importance to libraries. However, their application is far from trivial and the situation is further complicated by insufficiently understood difference between the two concepts. The paper reviews general approach implemented in both described doctrines, terminology issues, similarities and dissimilarities of the doctrines, their territorial coverage, and historic origins of doctrine differences. The doctrine having originated in the United Kingdom and developed in the United States has become an example, a pattern that is followed in legislation of many countries worldwide. Fair use/fair dealing concepts have found their reflection in Russian copyright law in the form of “free use” of a work without author’s permission and without copyright fee payment. The paper further deals with the significance of fair use doctrine for library collections digitization and other applications of technology innovation. A prediction is made for growing importance of fair use and fair dealing copyright exceptions in the nearest future.