An acceptable human pharmacokinetic profile increases the probability of a promising candidate drug becoming a successful therapy. The development of a mechanistic understanding of the disposition of candidate drugs towards confident predictions of key properties associated with human drug absorption, metabolism, distribution and excretion (ADME) is critical. This is achievable from a consideration of physicochemical properties, data from in vitro assays with human-derived material and from in vivo animal studies. This chapter is targeted at medicinal chemists and drug design teams and provides general definitions of the fundamental PK parameters together with best practice characterization, optimization and prediction strategies employed in the authors' laboratory.