This article focuses on the important instructional technique of integrated or interdisciplinary instruction with reference to the teaching of science but with implications for all school subjects. Readers are provided with a definition of the concept of the discipline and the importance of communicating the basic nature of a discipline to students in school settings. This leads to the concept of the levels of intradisciplinarity and later to the true "border crossing" that occurs when students must draw upon knowledge and practices from multiple disciplinary traditions when engaged in problem solving. The article concludes with a discussion of a recent trend in science instruction and consider the challenges of some forms of STEM curriculum designs.