This chapter discusses the complex analogy between biological evolution and technological innovation, focusing in particular on the novel construct modular exaptation. After carefully defining exaptation – a biological concept whose technological analogue is useful in innovation studies – the chapter explores its epistemological bases, arguing that the etiological concept of function – a biological tenet – is valid also in the technological domain. The complex analogy extends to biological and technological functional modules, providing the main building block on which modular exaptation can be founded. Establishing a complex analogy enables the description of the two domains via the same relational structure. In turns this allows the transferability of knowledge from the base domain to the target domain, and vice-versa. The complex analogy can therefore be considered a methodological tool for understanding complex systems in general and technological innovation in particular, as discussed in the final section of the chapter.