There is almost a consensus that tacit component of organisational knowledge is of critical strategic importance because, unlike explicit knowledge, it is both inimitable and appropriable. Because of its characteristics, organisational tacit knowledge is usually created and shared through highly interactive conversation and shared experience, i.e., through a socialisation process. At the firm's level, the effectiveness of the socialisation process depends on the firm's social capital. At group level, it has been argued that communities of practice form the basis of a firm's ability to create and share tacit knowledge. Therefore, investigating the relationship between social capital, communities of practice and individual human action is crucial in understanding the dynamic of cross level knowledge creation and utilisation and in understanding organisational learning process. In order to study this relationship Giddens' theory of structuration is used as it provides an integrating meta‑theory that recognises social reality as constituted by both subjective human actors and by objective institutional properties and attempts to articulate a process‑oriented approach that relates the realm of human action and institutional realm. Based on Giddens' theory a model of the interaction between human action and social capital of the firm is developed. According to this model such interaction is mediated through a firm's communities of practice, which are conceptualised as the means for realising the different types of modality between social capital and human action. Such conceptualisation of a firm's communities of practice as the means for realising the different types of modality between social capital and human action provides a fine‑grained approach to study the impact of their elements, i.e., shared repertoire, mutual engagement and joint enterprise, on the structural, relational and cognitive dimensions of a firm's social capital respectively. In addition, it explicates the duality of firm's communities of practice, namely: they are both the medium and the outcome of collective human action. This model also shows the need for further research in two areas. First is the study of the constraining roles of a firm's communities of practice in creating and sharing organisational tacit knowledge. Second is the study of social capital influencing organisational members in their relation to communities of practice.