This chapter provides an overview of what 'integrated STEM (Science, Technology, Engineering and Mathematics)' is-from its forms and characteristics to the practices and pedagogical approaches involved. It describes the forms of STEM integration followed by the hallmark characteristics of integrated STEM learning environment. STEM integration in the classroom generally takes one of three forms: content integration, supporting content integration, or context integration Content integration refers to units and activities that have multiple STEM disciplinary learning objectives. Context integration uses a context from one discipline to situate learning objectives from another discipline. Supporting content integration is common in the classroom, but often not done in a way that furthers the learning of the supporting content. Instructional approaches including problem-based learning and project-based learning, discussed in this chapter, are examples of the types of approaches conducive to teaching integrated STEM in K-12 classrooms. The biology provides important opportunities to discuss other aspects of K-12 engineering standards, for example ethics of cloning and genetic engineering.