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In division of wavefront, different spatial portions of an incident wavefront are selected and propagated so that their fields overlap. Double-slit interference is an example. The selected portions need sufficient spatial optical coherence for stable interference fringes.

In division of amplitude, one incident beam is split into two or more parts at a partially reflecting interface; they follow distinct paths and are recombined. The Michelson interferometer and thin-film interference use this principle. In division of wavefront, spatially distinct parts of the same wavefront are selected and allowed to overlap, as in double-slit interference. Both require adequate optical coherence; wavefront division particularly exposes the need for spatial optical coherence between the selected regions.