All transplanted individuals have frequent blood testing done; these include liver tests, including bilirubin, liver enzymes, and prothrombin time. Liver test abnormalities after orthotopic liver transplantation are frequent. Abnormal liver tests demand a search for the cause (or causes). Of critical importance is to understand the probabilities of certain liver or vascular injuries, which change as a function of the technical hurdles in performing the transplant, and time after transplantation. Mild elevations in the first few days after transplant are self-limited and do not require investigation. More severe early abnormalities may herald primary graft dysfunction or vascular thrombosis. Those occurring in the first few weeks draw attention to possible biliary complications, liver abscess, or bacterial or viral infection. This chapter provides context for understanding diagnostic possibilities.