The formation of the UiO-67 family of Zr MOFs is explored here through the prism of their acid-modulated growth, showing it to be key factor in controlling the MOF defect content, porosity, particle size, and morphology. The dynamic nature of the resulting Zr₆-monocarboxylate (”missing linker”) defect sites is explored for UiO functionalization (through acid exchange), “healing” and the introduction of a catalytically active M(III) cation.