As we will discuss in this review, to enable multiple catalysts to operate concurrently, issues relating to compatibility must be overcome. For example, potentially problematic catalyst-catalyst, catalyst-reactant, and catalyst-product interactions should be evaluated. To reconcile potential incompatibility, spatial and/or temporal control are needed to manipulate where and when certain processes occur. Spatial control may be employed to localize and separate catalysts or entire catalytic systems from each other. This may be achieved in a number of approaches (vide infra), namely compartmentalization, immobilization onto a surface, or by taking advantage of microscopic concentration gradients. . By preventing incompatible species from coming into contact with each other, efficient integrated processes may be promoted.