General aspects of disorder diffuse scattering are discussed. Diffuse scattering of crystals is due to deviations in space and/or time from an average structure of strict long-range order, where long-range order refers to three-dimensional translational periodicity. The iodine chain compound E 2 PI 1.6 serves as an example where the one-dimensional iodine substructure was studied by a quantitative analysis of extended diffuse layers. With this example general problems of a structure analysis by means of diffuse data are discussed. In urea inclusion compounds complicated order/disorder processes and subsequent phase transitions are related to longitudinal and lateral ordering within and between the urea host and the n-paraffin guest substructure. Combined X-ray and neutron methods help to clarify the static/dynamic origin of the diffuse scattering viz. disorder phenomena. Zirconia, ZrO 2 doped with various metal oxides, exhibits defect structures which decisively determine material properties. The defect structure can be interpreted by a quantitative analysis of diffuse data in the frame of a model of correlated microdomains. Diffuse scattering of quasicrystals (q.c.) is due to breaking of translational periodicity in N-dimensional space (N > 3), including fluctuations of sizes and shapes of (N-3)-dimensional 'hyperatoms'. Diffuse scattering of the (q.c.) decagonal phase AlNiCo indicates disorder with respect to one-dimensional translational and two-dimensional q.c. order. In particular, super-ordering and disordering within the q.c. arrangement are due to periodically ordered segments. Future trends of disorder diffuse scattering work are outlined.