A central objective of science education is to prepare students for the negotiation of science-related social issues (i.e., socioscientific issues) and to support them in reaching informed decisions. The ability to include both scientific and normative considerations into the negotiation has been summarized under the term socioscientific decision-making. Although socioscientific decision-making has been widely acknowledged as an essential component of students’ scientific literacy, difficulties remain concerning its promotion and assessment. In a first step, this dissertation outlines four challenges connected to the development of students’ socioscientific decision-making from a teaching-learning perspective (Challenge 1: The structure of the learning environment; Challenge 2: The complexity of socioscientific issues) and from a measurement perspective (Challenge 3: Conceptualization of socioscientific decision-making; Challenge 4: Assessment of socioscientific decision-making). To address the aforementioned challenges, three studies have been carried out as part of this dissertation. Each study aimed to extend the current knowledge about the development of students’ socioscientific decision-making in formal and non-formal learning opportunities. Study 1 comprises a systematic literature review, which considers empirical studies that explore the promotion of (1) students’ socioscientific decision-making in (2) sustainability-related and (3) extracurricular learning opportunities. Two different notions of socioscientific decision-making have been revealed as part of the results: Decision-making as a rational and mostly individual, and as a more cooperative, socially embedded process. Furthermore, no studies have been found with an equal distribution of attention among all three components. This shortcoming has been empirically investigated in Study 2, which assesses a sustainability-related extracurricular learning opportunity (an environmental science competition) in its effectiveness to promote participants’ socioscientific decision-making. The analysis of data supports the conceptualization of socioscientific decision-making as a multi-phased process; a conceptualization which has already been recognized among the science education community. On the other hand, the results from Study 2 confirm the presence of the two previously identified notions. The findings further suggest that participating in this science competition predominantly fosters the preparational phase of socioscientific decision-making. In contrast to Study 1 and Study 2, Study 3 focuses on formal learning opportunities (i.e., the regular classroom) and examines students’ argumentation as part of their decision-making process. The results of Study 3 provide evidence that an increase in issue familiarity does not enhance the diversity of argument types presented by students; however, the depth of already predominant types is manifested. Using both quantitative and qualitative methods, this dissertation provides novel insights into the promotion and assessment of students’ socioscientific decision-making by addressing the four previously identified challenges. The present work concludes with two final recommendations for contemporary science education. First, more attention should be paid to extracurricular learning opportunities, as they can empower students to investigate socioscientific issues that are meaningful to their lives. The second recommendation stresses the value of interdisciplinary working for the negotiation of complex socioscientific issues and thus the development of students’ socioscientific decision-making. """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""Note: The manuscript of Study 3 (pp. 91- 119) is a previous non-peer-reviewed version of an article which has now been accepted for publication in the International Journal of Science Education, published by Taylor & Francis: Garrecht, C. Reiss, M. J., & Harms, U. (2021). 'I wouldn't want to be the animal in use nor the patient in need' – The role of issue familiarity in students' socioscientific argumentation. DOI: 10.1080/09500693.2021.1950944