The present invention relates to blocking, inhibiting, reducing, antagonizing or neutralizing the activity of IL-17A, IL-17F, and IL-23. Antagonists include antibodies and antibody fragments that bind IL-23 and that bind IL-17A or IL-17F, such as antibodies that are cross-reactive for IL-17A and Il-17F. Antagonists that include an antibody or antibody fragment that binds IL-23 and an antibody or antibody fragment that binds IL-17A or IL-17F on one molecule are also disclosed. Antibodies and antibody fragments that bind IL-23 and IL-17F but that do not bind IL-17A are also disclosed. IL-17 and IL-23 are cytokines that are involved in inflammatory processes and human disease.