The "Next Generation Science Standards" (NGSS Lead States 20103) identify evidence-based argumentation as a key practice in science education. This argumentation comes in many forms, each providing a unique theoretical perspective and area of educational research. Argumentation can help model aspects of scientific culture and communities; engage students in the language and norms of science; develop critical-reasoning and justification skills; and coordinate evidence and theory in the science classroom. An important form of argumentation involves justifying a position on a socio-scientific topic. Socio-scientific issues (SSI) can help students understand how science is situated in, and influenced by, social contexts. Such issues are often controversial; involve competing views; and draw from fields as diverse as biology, ethics, sociology, economics, politics, and law. SSI instruction often uses complex, real-world case studies that don't have easy answers. In this article, the authors highlight an activities-based curriculum designed to foster socio-scientific argumentation. They also discuss the particular importance of ethical considerations and stakeholder viewpoints in socio-scientific arguments.