Scientific reasoning and scientific argumentation are highly valued outcomes of K-12 and higher education. In this article, we first review main topics and key findings of three different strands of research, namely research on the development of scientific reasoning, research on scientific argumentation, and research on approaches to support scientific reasoning and argumentation. Building on these findings, we outline current research deficits and address five aspects that exemplify where and how research on scientific reasoning and argumentation needs to be expanded. In particular, we suggest to ground future research in a conceptual framework with three epistemic modes (advancing theory building about natural and social phenomena, artefact-centred scientific reasoning, and science-based reasoning in practice) and eight epistemic activities (problem identification, questioning, hypothesis generation, construction and redesign of artefacts, evidence generation, evidence evaluation, drawing conclusions as well as communicating and scrutinizing scientific reasoning and its results). We further propose addressing the domain specificities and domain generalities of scientific reasoning and argumentation as well as approaches for facilitation. Finally, we argue for investigating the role of epistemic emotions, the role of the social context, and the influence of digital technologies on scientific reasoning and argumentation.