Nanocellulose is an exceptional biomaterial whose industrial applications in widely different sectors and technologies so far were chiefly limited by the high cost of its multi-step extraction routes. Extraction methods of cellulose nanocrystals or nanofibers, indeed, generally involve energy-intensive mechanical treatment of  wood pulp,  treatment with concentrated H2SO4 to obtain cellulose nanocrystals, or chemical oxidation of the nanofibers followed by mechanical fibrillation of the partly oxidized fibers. In the last decade (2011-2021) a number of new green routes to cellulose nanofibers and nanocrystals have been developed. This study provides a critical outlook of such emerging green new routes to this versatile and safe bionanomaterial that once sustainably produced, preferably from low cost cellulosic biowaste, will become uniquitous in a number of different industrial products.