Technology Intensive (TI) firms often customize their offerings through engineer-to-order projects. However, intensified competition and technological developments drive them to become more efficient. Following trends in consumer markets, many TI firms turn to modularity. Yet, while previous research has examined customization in consumer settings, it remains unclear what the impact of customizing through modularity is for TI firms in business-to-business markets. This study synthesizes the various types of customization proposed in the literature with respect to modularity and complements these with findings from a qualitative field study. A grounded typology of four offerings demonstrates that these represent different levels of combining customization and modularity. Important antecedents add to our understanding why TI firms increasingly follow a specific approach. We extend this through identifying managerially relevant challenges