Domain aspects of multi-ferroics are reviewed, i.e. of materials in which two or all three of the properties ferroelectricity, ferromagnetism, and ferroelasticity occur simultaneously in the same phase, and in which the magnetic point group has been reliably established by magnetoelec., optical, dielec., magnetic and related studies on single crystals and single domains. Nearly only members of the boracite crystal family are concerned, whereas for the perovskite family and other classes of material there is great paucity of data on single crystals. Polarized light microscopy is shown to be an indispensable tool for the study of multi-ferroics, in particular when ferroelasticity is involved. Potential multi-ferroic magnetoelecs., so far only known in ceramic form, are excluded from the survey. 106 Refs.