Immunogenicity can be a major obstacle to successful protein drug therapy. Antidrug antibodies may neutralize therapeutic function, influence pharmacokinetics and, in some cases, lead to severe adverse effects. These effects depend on factors including dose, regimen, delivery route and contaminants, among others. Importantly, immunogenicity is a consideration that is better addressed during preclinical development before complications arise in clinical trials or following licensure. This article will address the development and application of computational tools for immunogenicity assessment of protein therapeutics, and validation of those predictions using peripheral blood from exposed subjects or alternative in vivo methods.