IgG antibodies are the basis of some of the most effective therapeutics developed over the last 20 years. These antibodies are highly specific, have long serum-half lives, and can be produced relatively routinely, making them ideal drugs for immunotherapy. The degree of regulation on IgG antibody effector functions by the composition of the single, N-linked glycan attached to the Fc is increasingly appreciated. IgG antibodies with identical protein sequences can gain a 50-fold potency, in terms of initiating antibody-dependent cellular cytotoxicity (ADCC) by removal of the single fucose residue from the Fc glycan. Conversely, the addition of sialic acid to the terminus of the Fc glycan converts IgG antibodies into anti-inflammatory mediators, capable of suppressing autoantibody driven inflammation. This review will discuss the contribution of the Fc glycan to IgG antibody effector functions, the regulation of the antibody glycosylation in vivo, implications for the rational design of IgG antibody-based therapeutics, and touch upon the contribution of glycosylation to other immunoglobulin isotypes.