During the past few decades, much of the experimental and clinical effort in solid-organ transplantation has been directed toward ameliorating or abrogating T-cell-mediated responses. As a result, universally understood and accepted nomenclature and diagnostic criteria have evolved. Humoral immunity in transplantation has yet to undergo a similar renaissance. Readers of transplant journals regularly find it difficult and often impossible to interpret data on the diagnosis and management of antibody-mediated rejection. The Antibody Working Group was assembled in an attempt to provide guidelines for the standardization of nomenclature, diagnostic criteria, reporting, antibody profiling, and risk assessment.