To date, more than 20 recombinant immunoglobulin G (IgG) antibody therapeutics are licensed for the treatment of various diseases. The mechanism of action of recombinant monoclonal antibodies (rMAbs) has been extensively investigated and several distinct pathways have been defined; selective activation of specific pathways may optimize clinical outcomes for different diseases, such as cancer and chronic inflammation. Human IgG is a glycoprotein with oligosaccharides attached at a single site. These are essential to the mode of action of rMAbs, and the antibody efficacy can vary depending on the particular oligosaccharide that is attached. Methods are now becoming available that allow the production of rMAbs bearing pre-selected oligosaccharides - glycoforms - to provide maximum efficacy for a given disease indication. This Review summarizes current knowledge of these methods and avenues for their exploitation in the clinic.