This paper will summarize the clinical features of transfusion-related acute lung injury (TRALI) before the experimental and clinical literature on the pathogenesis of TRALI is reviewed. Several mechanisms by which leukocyte antibodies induce TRALI have been unraveled. Significant advances have also been made in the field of recipient-related factors that contribute to the development of TRALI. In contrast, the pathomechanism behind non-immune TRALI (associated with the transfusion of blood components which do not contain antibodies) is less well understood, especially since the relevance of mechanisms proposed earlier is questioned by recent findings. The diversity of newly described factors contributing to TRALI supports the previously proposed threshold model of TRALI, and an extension of that model including newly defined multipliers and attenuators of TRALI is emerging.