This chapter closes this edited volume on Non-Formal and Informal Science Learning in the 21st Century. Through an ecosystem perspective, we aim to understand and represent the interrelationships among the ecosystem elements that provide actors with avenues by which they may be introduced to and become knowledgeable about science and science learning. This is particularly relevant for non-formal and informal learning contexts since actors engage in science learning activities outside the formal learning context, and therefore they are not (necessarily) learning and teaching professionals, and also science education is not (necessarily) their main objective (e.g., when in informal learning contexts). In addition, actors are different from one another; therefore, it is necessary to take into consideration their attributes and beliefs to better understand their behavior, their capabilities, and their needs, which in turn will improve efficiency, coherence, and performance of the ecosystem overall. The overarching goal of this chapter is to present a conceptualization of informal and non-formal science education through an ecosystem model and propose a research agenda for the future. By doing this, the chapter seeks to offer a broader foundation for paving the way toward a holistic understanding of Non-Formal and Informal Science Learning in the 21st Century.