Legitimacy is crucial for firms, but previous studies only focused on one stage of their life cycle. This article uses the cooperate life cycle theory to explore the types of legitimacy firms need at different stages to improve performance. The study tested 496 IT firms and found that cognitive, normative, and regulative legitimacy play different roles across the life cycle. Having the right strategy at each stage helps firms gain the proper legitimacy, leading to better performance. A case study on 58.com in China confirmed these findings. This research expands on legitimacy theory for firms and offers practical advice for firms to obtain the right legitimacy at each life cycle stage.