Interleukin-18 (IL-18) participates in both innate and acquired immunity. The bioactivity of IL-18 is negatively regulated by the IL-18 binding protein (IL18BP), a naturally occurring and highly specific inhibitor. This soluble protein forms a complex with free IL-18 preventing its interaction with the IL-18 receptor, thus neutralizing and inhibiting its biological activity. The present invention discloses binding molecules, in particular antibodies or fragments thereof, which bind IL-18 and do not bind IL-18 bound to IL-18BP (IL-18/IL-18BP complex). Apart from its physiological role, IL-18 has been shown to mediate a variety of autoimmune and inflammatory diseases. The binding molecules of the inventions may be used as therapeutic molecules for treating IL-18-related autoimmune and inflammatory diseases or as diagnostic tools for characterizing, detecting and/or measuring IL-18 not bound to IL-18BP as component of the total IL-18 pool.