Among the class of zwitterionic polymers poly(carboxybetaine)s (poly(CB) s) are unique, emerging as the only ultra-low fouling materials known allowing the preparation of biosensors, fouling resistant nanoparticles, and non-adhesive surfaces for bacteria. Poly(carboxybetaine methacrylate) and poly(carboxybetaine acrylamide) have been prepared via atom transfer radical polymerization (ATRP), however a polymerization with living characteristics has not been achieved yet. Herein, the first successful living/controlled reversible addition fragmentation transfer (RAFT) polymerization of (3-methacryloylamino-propyl)-(2-carboxy-ethyl)-dimethyl-ammonium (carboxybetaine methacrylamide) (CBMAA-3) in acetate buffer (pH 5.2) at 70 and 37 degrees C is reported. The polymerization afforded very high molecular weight polymers (determined by absolute size exclusion chromatography, close to 250 000 g . mol(-1) in less than 6 h) with low PDI (<1.3) at 70 degrees C. The polymerization was additionally carried out at 37 degrees C allowing to achieve yet lower PDIs (1.06 <= PDI <= 1.15) even at 90% conversion, demonstrating the suitability of the polymerization conditions for bioconjugate grafting. The living character of the polymerization is additionally evidenced by chain extending poly(CBMAA-3) at 70 and 37 degrees C. Block copolymerization from biologically relevant poly[N-(2-hydroxypropyl)methacrylamide] macroCTAs was additionally performed.