Photochemical processes leading to the photoinduced anisotropy and the excellent photoaligning properties of bis-methacrylic polymers are discussed. Comparing the data for bis-methacrylic polymers and a series of model compounds, we conclude that Fries rearrangements and crosslinking reactions taking place in bis-methacrylic polymers cause the photoinduced ordering in films of these polymers via the mechanism of photoselection. Thus, all of these photochemical processes contribute to the liquid crystal photoalignment. The induced alignment is thermally stable due to the crosslinking of methacryloyl groups which fix the induced anisotropy in aligning polymer films.