The role of complementary products is becoming increasingly important in facilitating innovation and has become a pivotal aspect of an organisation’s technology strategy. To address the lack of a useful framework that captures the different dimensions of product complementarity, this paper proposes a categorization for complementary products centered on user engagement. Based on a sample of 305 make, buy, and ally decisions for 32 primary product firms in the Personal Computing industry, this paper explores the influence of the proposed categorization on its strategy decision for developing complementary products. Results suggest a nuanced categorization of product complementarity adds value to explaining the decision, with the firm’s knowledge capital having a non-trivial influence on it. This paper endeavors to contribute to the literature on platform innovation by examining significance of inter-product relationships on strategy.