The dictionary definition of constraint is one-sided, solely restrictive. The problem-solving definition is two-sided. Constraints come in pairs. One retains its restrictive function, precluding something specific; the other directs search for its substitute. The paired constraint model is applied to both domain and classroom. I discuss the effects of curricular, variability, testing, cognitive, and talent constraints; demonstrate how paired constraints can be used to create a new curriculum; and close with suggestions for using constraints effectively and creatively in the classroom.