Open innovation can support firms looking to deploy strategic agility through product innovations during periods of market and technological change. However, existing research lacks a comprehensive understanding of the microfoundations that underlie strategic agility in the context of open innovation. We address this gap using an in-depth analysis of a firm's open innovation activities in support of new product development (NPD). Our analysis reveals that open innovation can help leverage NPD processes to drive technological innovations in response to changing market conditions. Under such circumstances, open innovation enables firms to deploy strategic agility by continually developing the product portfolio. Our study reveals six mechanisms that enable three mutually complementary practices of agility: knowledge-based agility at the firm-environment interface, behavioural agility in the firm's decision-making process, and organisational agility in the internal NPD process. We theorise the interplay between the mechanisms that constitute each practice and, in doing so, shed light on how they contribute to firm-level strategic agility.