To date, there is no consensus on how to assess functional impairment in individuals with mild cognitive impairment (MCI), and this lack of consensus is reflected in the clinical practice. Since the criterion used in the literature is very vague, clinicians are still left without much guidance in this area. Thus, the main goal of this study was to examine how functional impairment in individuals with MCI has been assessed in the literature. An electronic database search strategy was developed in consultation with an experienced librarian. Four databases (CINAHL, PsycINFO, PubMed, and MEDLINE) were searched from 2000 to May 2014 to provide a comprehensive coverage of the literature. The literature search yielded 14 tools that assessed functional impairment in MCI. Among those, nine tools were performance-based measures in which participants were observed while executing a task in a simulated environment using real life material. In terms of questionnaires (either informantor self-reports), five tools were found. Different functional domains have been assessed in each tool. According to this review, the characteristics of the instruments used in the literature to assess functional impairment in individuals with MCI vary greatly. Nonetheless, results of this study allow clinicians to make better-informed decisions when choosing a functional assessment for this population.