Modularization involves breaking up a system into discrete chunks, which communicate with each other through standardized interfaces, rules, and specifications. It is a broad concept with various interpretations and meanings across research disciplines. The complexity and scope of a module is not captured sufficiently and clearly in the construction management and engineering literature, and the impact of modularization across project phases has not been fully explored and articulated. Therefore, the main question addressed in this paper relates to the inherent meaning of what is a module in the context of different phases of a building project. In addressing this question, this paper empirically investigates the use of modularity in 15 construction projects situated in Italy, Germany, Brazil, and the United Kingdom. The findings of this research suggest that a design-based and an operations-based perspective of modularity coexist, and that there is the need for an integrated view of modularity across the project lifecycle phases and for collaborative working between designers and site operators. To this aim, a unifying definition of a module in building projects is proposed along with a practical guide to help managers organize project activities for effective modularization. The actual cost analysis of the various modularization strategies provides an interesting avenue for future research. The template proposed also requires wider testing with a wider range of modules.