This paper is a review of current scientific literature in the area of social isolation and health in both humans and nonhuman animals. Social isolation is an important subject today with social isolation generally increasing throughout human populations across the globe. Animals offer critical insights into certain mechanisms of social isolation. While assessing social isolation in animals is quite different in comparison to humans, the results of experimentation often show that animals share similar biological responses to social isolation with humans. Areas of social isolation research assessed in this paper include social isolation terms, methods and/or measurement, interventions (including environmental enrichment in animals), and biopathology. While some comparative studies exist that compare social isolation in humans and animals, this paper attempts to be a summative analysis of literature in multiple specific areas of social isolation research. The purpose of this literature review is to provide a perspective of first how social isolation is defined, of how it is measured, and finally the significance of both humans' and animals' biological responses to social isolation. Of these areas, comparisons between humans and animals offer critical insights for future social isolation research.