Supply-side innovators play an important role in both the sustainability of a platform and increasing the number of its users. However, existing platform-related studies have mostly focused on the demand-side perspective and the few supply-side studies have ignored the complementors' innovation processes (CIPs). Moreover, recommendations in the innovation management literature usually address large manufacturing companies. Taking into account that an appropriate innovation process is context-dependent, the currently available general recommendations may not be particularly effective for complementors' innovations. This paper aims to identity CIPs and to explore the rationale behind them. This research is comprised of small, Iranian companies in the software industry. The paper uses a qualitative approach and utilizes an exploratory multiple case study method. Data is collatet using 35 semistructured interviews with 23 small companies that develop Android/IOS based applications. Secondary information, including news and interviews published in web concerning the innovation of the companies is utilized as well, in onder to supplement the interviews. The collected data is analyzed based on the qualitative content analysis and constant comparative methods. The findings indicate three processes for complementors' innovations and reveal that the important contingencies affecting these processes are: perceived technical and business complexity.