What is the unique nature of social capital that differentiates itself from other forms of capital? How should we conceptualize and operationalize social capital? What are the major drivers and outcomes of social capital? To address the three questions, I apply the duality lens—the perspective of regarding each entity as a paradox consisting of two contrasting yet interdependent components—to social capital for an integrative model of informal exchange. The focus of this paper is on the duality relationship between the content variables (social tie, social capital, social behavior along two basic dimensions: trust for tie strength and option for network structure) and the process variables (antecedent, content, process, and consequence) toward a geocentric framework of formal–informal exchange. I intend to make two contributions. First, the conceptualization and operationalization of social capital is developed from the duality lens of formal–informal exchange so as to identify the unique nature of social capital as an informal entity. Second, a holistic, dynamic, and dialectic model of social capital is provided to explore the causal links between various elements related to social capital. Copyright Springer Science+Business Media, LLC 2007Social capital, Trust, Option, Tie strength, Network structure, Informal exchange,