In the first part of this article, three examples of microdomain fixing in sequential copolymer films are reviewed. Two of them are examples of chemical fixation of the microdomains, and at the same time making the films insoluble in solvent. Quaternization by a gas-phase dibromo compound or photosensitizing polymerization was chosen in these cases. Another example is concerned with the crosslinking of isolated domains in graft copolymer matrix. By this reaction, small particles of the different materials of which the outside and the inner core are composed are expected to be obtained. Actually until a rather high crosslinking density (4.2 mol%), soluble products were obtained, and these materials differed from the original graft copolymer. In the second part, micelle formation with sequential copolymers in selective solvents, their dimensions, form, and so forth are reviewed with reference to the crosslinking of the core part. Finally, several results obtained with graft copolymers in recent years are reported.