Magneto-Science, a new science of materials using magnetic fields, is recently being developed all over the world. Magneto-Science concerns mainly feeble magnetic materials such as soft matter, carbons, ceramics, and organometals. Colloidal and interfacial systems under magnetic fields are very attractive and important because the dimensions are very much sensitive to magnetic fields. In this review we introduce several examples in colloid and interface chemistry under magnetic fields. Molecular assemblies such as micelles, bimolecular membranes, and vesicles are changed in shape and, in some cases, size and composition by magnetic fields. Since mesophases are sensitive to relatively low magnetic fields, magnetic fields control not only structures and functions but also cooperatively other magnetically insensitive materials. Moreover, a few interesting magnetic responses in hydrogels are summarized.