This open-label clinical trial will evaluate the pharmacodynamics, pharmacogenomics and early efficacy and safety of steroid-free Tacrolimus (TAC) monotherapy and its minimization after induction with rabbit, anti-human thymocyte globulin (rATG, Genzyme, Cambridge, MA) in children and adults with pediatric liver transplantation. Eighty subjects (0-21 years) receiving liver transplantation will be enrolled. Incidence and severity of biopsy-proven acute cellular rejection (ACR) is a primary endpoint as well as time to Tacrolimus whole blood concentrations <8 ng/ml The expected incidence of ACR is 50% and is derived from a non-consecutive subject population (n=40) who received an identical regimen in Investigational New Drug (IND) 64555. This incidence is acceptable because the long term sequel of rejection reported with other allografts have not been observed in liver grafts during IND 64555. These risks are further negated by the unique regenerative capacity of the liver allograft. An OBSERVATIONAL arm is being included in this trial. Because the numbers of pediatric liver transplants (LTx) are small in any single center setting, no information is known about relative outcomes on a conventional protocol, in children receiving conventional protocol of steroids+Tacrolimus. The PURPOSE of this additional recruitment is OBSERVATIONAL, only. Therefore, these subjects will NOT be randomized. Rather, by studying all types of patients, we hope to utilize maximally, all available subjects, to understand the relative place of monotherapeutic induction. In turn, this will be the basis for a follow-up comparative, randomized trial.