Wildlife management and conservation biology are full of conflict, especially in regard to introduced vertebrates in Hawai`i. At present, there are 17 introduced mammals with established wild populations in Hawai`i, including 6 ruminants, 4 rodents, 3 feral pets, pigs, donkeys, rock wallabies, and mongooses. Disagreement about the reliability of information on the impacts of introduced mammals in Hawai`i is one reason for conflict between stakeholders, which may undermine conservation and management programs. The objective of this research was to assess what science has recorded in regards to the impact of introduced mammals on the native flora, fauna, and ecosystems of the Hawaiian Islands. A literature (peer-reviewed articles, theses, dissertations, and grey literature) search for data on the impact of these species resulted in 156 articles, which were assigned to 1 of 6 categories that describe science’s ‘Level of understanding’ of the impacts of mammals in Hawai`i. The vast majority of the available data (134/156 articles) resulted from basic observations or general exclosure plots. In terms of their impact in Hawai`i, cats (21 articles), black rats (27 articles), and pigs (40 articles) are the most researched and hence best understood species. Very little is known about the impacts of dogs, rabbits, brush-tailed rock wallabies, and donkeys on the flora, fauna, and ecosystems of Hawai`i. Analysis of the dates of publication of articles suggests research may be influenced by the level of controversy surrounding a species.