This article presents the Psycho-Ecological Systems Model (PESM)--an integrative conceptual model rooted in General Systems Theory (GST). PESM was developed to inform and guide the development, implementation, and evaluation of transdisciplinary (and multilevel) community-engaged scholarship (e.g., a participatory community action research project undertaken by faculty that involves graduate and/or undergraduate students as service-learning research assistants). To set the stage, the first section critiques past conceptual models. Following a description of GST, the second section provides a comprehensive description of PESM, which represents an integration of three conceptual developments: the ecological systems model (Bronfenbrenner, 1979), the biopsychosocial model (Kiesler, 2000), and the principle of reciprocal determinism (Bandura, 1978). In the third section, we discuss implications of PESM for community-based research. A greater emphasis on the development of integrative conceptual frameworks may increase the likelihood that community-based research projects will: (a) address complex questions; (b) develop and implement efficacious (and sustainable) transdisciplinary (and multilevel) projects; (c) assess constructs at multiple levels using a blend of quantitative and qualitative approaches; and (d) utilize multiple research designs and methods to systematically examine hypotheses regarding a project's influence on outcome variables and process variables.