This article considers modular composition as an approach to engendering structural plasticity in musical works. Structural plasticity, in this case, is defined as the ability for the components of a musical work (e.g., events, ideas, sequences, textures, timbres) to vary in how and when they are presented. In this research, modular composition is the process for creating a collection of individual musical ideas (e.g., sequences, patterns, phrases) termed ‘modules’, and designing a dynamic system for their assembly into cohesive structures. This approach results in musical works that exist in a state of constant structural flux, allowing for real-time alteration while progressing beyond similar existing approaches observed in video game music and interactive music apps, from which this research takes inspiration. Approaches involving compositionally focused intelligent music systems are also observed, highlighting how modular composition bridges traditional compositional practices and the design of interactive music systems. Two of the authors’ own works are discussed with regard to how modular composition can be implemented in varying creative ways. The outcome of this work illuminates the creative possibilities of integrating traditional compositional practices with new digital approaches to arrive at a more structurally plastic and alterable form of music.