Techniques based on magnetooptical rotation have recently been of great use in the study of metamagnetic crystals. Under achievable conditions this rotation is a measure of M which may be measured automatically as H or T vary. The distinctly different rotations of coexisting anti‐ and paramagnetic phases at the first order metamagnetic transition make possible direct examination of the mixed state with a polarizing microscope. Furthermore, many properties of mixtures of the two time reversed antiferromagnetic states may be deduced from their appearance in applied fields. Two metamagnets have been studied: FeCl2: TN?23.5 K, layer structure with competing ferromagnetic intra‐ and antiferromagnetic interlayer interactions.Dy3Al5O12 (DAG): TN?2.54 K, garnet structure rich in symmetry properties. There are magnetooptical manifestations of coupling between the antiferro‐magnetic order parameter and fields along [111].Moving pictures will be shown on the metamagnetic transition in DAG and FeCl2 as well as that b...