What is typical of a vocational curriculum is that it is a course of learning across different school- and work-based practices. This chapter discusses such learning in terms of boundary crossing between these practices. We conceptualize boundaries as sociocultural differences that lead to discontinuity in action or interaction. Such discontinuities between school and work practices have frequently been reported as problematic. Boundary crossing is defined as the efforts by individuals or groups to establish or restore continuity in relation to action or interaction across practices. As this chapter argues, these efforts point to the learning potential of boundary crossing between school and work practices, which we summarize in terms of four learning mechanisms: identification, coordination, perspective making and taking (or mutual reflection), and transformation. These learning mechanisms are discussed through illustrations from vocational education and training. The chapter concludes by speculating on what would be fruitful boundary analyses of situations where a vocational curriculum could be improved.