Theorising plays a foundational role in Information Systems (IS) research. While the field has made important advances through theory borrowing, via adaptation and instantiation, as well as through contextualisation of established frameworks and models, comparatively little attention has been devoted to the elaboration of existing theories through structured, logic-driven approaches. This commentary problematises that imbalance and advances the concept of deductive theory elaboration as a valuable, yet underutilised, form of theorising in behavioural IS research. We define deductive theory elaboration as a process that extends existing theories by introducing conceptual modifications to their constructs, relationships, or boundary conditions prior to empirical testing. We distinguish this approach from related forms of theorising and propose a four-step framework supported by a repertoire of elaboration patterns for both variance and process theories. We also offer practical reporting guidelines to promote transparency and rigour in elaboration-based contributions. Our aim is to encourage more systematic elaboration efforts to enhance the precision, generalisability, and cumulative potential of IS theories, an optimistic vision of how behavioural IS research can evolve to meet the conceptual challenges of a rapidly transforming digital landscape.