Scholarship on complex systems in the learning sciences has mirrored research in real world scientific investigation to support learning about how natural (e.g., climate) and human-made (e.g., power grids) systems exist, fluctuate, and can be made more robust. Learning sciences research has demonstrated that students find learning about complex systems challenging often due to hidden system structures and dynamics such as micro-level behaviors that give rise to macro-level emergent patterns. This chapter reviews what we know about students’ understanding of complex systems, conceptual frameworks for building curricular and instructional strategies to improve learning, tools and interventions that are used to support those frameworks, and suggestions for future development and growth in learning sciences research about the teaching and learning of complex systems.