The lack of core theories is a challenge for the whole software engineering (SE) discipline, particularly crucial for the agile software development (ASD) field, which is largely practice-driven. Without solid and continuous theoretical development glued by core theories, ASD risks repeating wrong practices and oversimplifying real-world phenomena. To address this issue and foster a strong link between empirical evidence and theoretical development, we conduct this critical review using the Complex Network Analysis (CNA) approach, in response to the editors’ call on the XP2020 conference. Based on 83 selected articles and 88 identified theories, our analysis traced the originating disciplines of these theories and synthesized 3 key theory communities. We position ASD core theories between empirical generalization and middle-range theories in the SE theory spectrum and offer practical guidelines for researchers to use, borrow, and generate ASD theories. It is further recommended that new theory development be aligned with the theory of coordination and control theory while employing Complex Adaptive Systems (CAS) theory as a theoretical lens when borrowing theories to ASD.