Pharmacokinetic-Pharmacodynamic (PK/PD) modeling is scientific mathematical tool which integrates relationship PK model to that of PD model and a statistical model (particularly, the intra- and inter-individual variability of PK and/or PD origin). PK-PD approach is used from initial preclinical stage to last clinical phases for exploring the concentration-effect relationships executed using various approaches, such as steady state concentrations versus non-steady state concentrations models and parametric versus nonparametric models. Basing on the concentration-response invariant data basic models such as fixed-effect, linear, log-linear, Emax and sigmaoid Emax models are used. But in case of time-concentration and time-response variant conditions effect compartment, acute tolerance, sensitization and physiological indirect response models have been used. PK/PD modeling can be used as an applied science tool to provide answers on efficacy and safety of new drugs faster and at a lower cost. Still limits of PK/PD approaches include the development of appropriate models, the validity of surrogate endpoints, and the acceptance of these models in a regulatory environment.