Conventional 3-D printing processes are material-dependent and irreversible. We are working on an alternative approach based on 3-D assembly of mass-produced 2-D components of digital material. This significantly enlarges the available material set, allows reversible disassembly, and imposes constraints that reduce the accumulation of local positioning errors in constructing a global shape. Experimental work on material properties and dimensional scaling of the digital material leads to application in assembling functional structures. We propose that assembling digital material will be the future of 3-D free-form fabrication of functional materials.