This study explores the use of the systems approaches (systems thinking and systems theories) as the theoretical underpinnings for Enterprise Architecture (EA) research. Both the academic and the practitioner communities have maintained an interest in EA due to its potential benefits, promising for the recent technological and business advances. EA as a research area is, however, characterized by diversified views depicted in different definitions of the concept, and no acknowledged common theoretical foundation. A number of prior studies have noticed this gap in the EA field of research, and called for a strengthening of the theory of EA. Variegated systems approaches have been suggested as a theory base. The aim of this study is to examine if, and to what extent the systems approaches could provide a common theoretical foundation. We contribute with a systematic literature review on the state-of-art of systems approaches in EA research. We find that the systems approaches are, indeed, frequently referred to in the EA studies. However, as of yet, the application of these theories appears to be fragmented, and the approaches are rarely systematically used in empirical studies. We discuss the findings, reflecting to the types of theory and the use of theory in our area of research.