After the first decade of QSAR in mid 1970s, it was observed that relationship derived from a series of compounds investigated in isolated systems did not apply to in vivo situations. Hence, it was realized that ADME processes of a drug were important determinants, as these modulated the concentration-time profile of the drug substance at the drug receptor site. Indeed, lack of activity may not be due to low affinity of a drug for the receptor, but an inadequate concentration of the drug at these sites. The introduction of pharmacokinetic parameters permitted markedly better interpretation of the structure-activity correlation in physiological and biological terms. Development of QSPR amongst congeneric drug series not only saves considerable amount of time, money, animal life and involvement of "normally, healthy and drug-free human volunteers" required for conducting experimental pharmacokinetic studies, but also the expertise of pharmacokinetists and drug designers. Therefore, this book may prove useful for those who want to explore such techniques for the determination of ADME properties of a chemical compound before being actually introducing into human volunteers.