This paper explores the relationship between economic integration and endogenous growth, focusing on two similar, developed economies. The authors consider two models with different specifications of the research and development (R&D) sector, which is the source of growth. They argue that economic integration can increase the long-run growth rate if it encourages the exploitation of increasing returns to scale in the R&D sector. The paper discusses the effects of trade in goods and flows of ideas on growth, highlighting that both can lead to a permanent increase in the worldwide growth rate. The authors also examine the implications of different R&D specifications, such as the knowledge-driven and lab equipment models, and the role of scale effects in economic integration. The paper concludes by discussing the limitations and extensions of the models, emphasizing the need for further research to refine the understanding of the complex dynamics between economic integration and growth.This paper explores the relationship between economic integration and endogenous growth, focusing on two similar, developed economies. The authors consider two models with different specifications of the research and development (R&D) sector, which is the source of growth. They argue that economic integration can increase the long-run growth rate if it encourages the exploitation of increasing returns to scale in the R&D sector. The paper discusses the effects of trade in goods and flows of ideas on growth, highlighting that both can lead to a permanent increase in the worldwide growth rate. The authors also examine the implications of different R&D specifications, such as the knowledge-driven and lab equipment models, and the role of scale effects in economic integration. The paper concludes by discussing the limitations and extensions of the models, emphasizing the need for further research to refine the understanding of the complex dynamics between economic integration and growth.