This paper applies irreversibility analysis to characterize humidification-dehumidification (HD) desalination cycles and to identify how to further improve cycles and components. It is shown that minimizing specific entropy generation of the cycle maximizes the gained output ratio (GOR). It is also shown that each cycle has one limiting component that cannot be substantially improved and a second component that should be the target of efforts to minimize entropy generation. Finally, the failure of exergy analysis to yield conclusive results for on-design HD cycle analysis is discussed briefly.Center for Clean Water and Clean Energy at MIT and KFUPM