The protein transition, aimed at rebalancing protein intake between animal and alternative sources, is gaining traction in scientific and policy discussions on food system transformation. This systematic review identified 33 articles addressing challenges in reducing the environmental impacts of protein production and consumption, providing healthy diets for a growing population, and preventing adverse effects of industrial livestock production systems. The review found unclear definitions of the protein transition, conflicting views on reduction or replacement of dietary protein, and a lack of attention to systemic change. Three main narratives emerged: the consumer narrative focusing on consumption-based solutions, the techno-centred narrative developing more resource-efficient protein production systems, and the socio-technological narrative transitioning the agri-food system from an animal-dominated regime to an alternative protein regime. The review concludes that solutions should consider factors such as scale, initiating actors, and expected impact to support complementary protein transition approaches. The protein transition is crucial for environmental sustainability, human health, food security, and animal welfare, but it lacks a consistent definition, which can lead to misalignment with core challenges and ineffective solutions. A well-crafted definition is essential to facilitate engagement from diverse stakeholders and ensure that solutions effectively address the identified challenges.The protein transition, aimed at rebalancing protein intake between animal and alternative sources, is gaining traction in scientific and policy discussions on food system transformation. This systematic review identified 33 articles addressing challenges in reducing the environmental impacts of protein production and consumption, providing healthy diets for a growing population, and preventing adverse effects of industrial livestock production systems. The review found unclear definitions of the protein transition, conflicting views on reduction or replacement of dietary protein, and a lack of attention to systemic change. Three main narratives emerged: the consumer narrative focusing on consumption-based solutions, the techno-centred narrative developing more resource-efficient protein production systems, and the socio-technological narrative transitioning the agri-food system from an animal-dominated regime to an alternative protein regime. The review concludes that solutions should consider factors such as scale, initiating actors, and expected impact to support complementary protein transition approaches. The protein transition is crucial for environmental sustainability, human health, food security, and animal welfare, but it lacks a consistent definition, which can lead to misalignment with core challenges and ineffective solutions. A well-crafted definition is essential to facilitate engagement from diverse stakeholders and ensure that solutions effectively address the identified challenges.