There are many educational strategies to achieve learning objectives to prepare students to adapt and survive more effectively in life. Many of these approaches involve, to some degree, practical learning experiences structured to emulate meaningful situations, tasks, and the problem solving required of the real world. In science, educators have long held and place particular importance in the idea that hands-on experiential activities are a fundamental tenet of learning. The portion of scientific instruction devoted to learn by ‘doing’ is called ‘practical work’. In this chapter, we explore the concept of practical work in science instruction, including categories of practical work, the historical basis and development of practical work, its purpose and value, controversies concerning practical work’s utility in science instruction, the importance of practical work in online science instruction, and the design of practical work learning environments. This chapter builds a rationale for the broad value and integral importance of practical work in science education at both the K-12 and university level and as such the necessity for its intentional implementation in online science learning environments. In this way, the practical work discussion of Chapter 5 provides the underpinnings to later chapters that review current and emerging forms and technologies to support online practical work.