The global transition toward sustainable energy has become critical due to climate change, diminishing fossil fuels, and increasing demands for renewable solutions. This transition requires more than technical solutions; it demands an integrated approach that incorporates Business Model Innovation (BMI) and Business Ecosystem Innovation (BEI) to support sustainable practices. This chapter explores how BMI and BEI are related in the context of the sustainable energy transition, applying a framework based on three key elements of business model design: content, structure, and governance. The research presented in this chapter is based on a qualitative case study of the business ecosystem of the sustainable energy transition. Data were collected from 26 semi-structured interviews conducted with key actors involved in the energy transition in Finland and Sweden. The findings reveal that BMI initiates BEI by introducing new technologies, fostering cross-sector partnerships, and driving complementary innovations. In turn, BEI stimulates BMI by providing resources, reshaping market conditions, and encouraging firms to align with ecosystem-wide sustainability standards. This study contributes to the theoretical understanding of BMI by extending its scope from a traditional firm-centric view to considering ecosystem-wide impacts, thus addressing calls for a broader perspective on BMI’s systemic effects. It also highlights the strategic advantages of aligning Business Model Innovation with ecosystem objectives for firms to leverage cross-sector partnerships and foster collaboration for enhanced innovation and resource efficiency.