The objective of this chapter is to provide the reader who may already have some HPLC experience with a logical approach to the optimisation of a chromatographic separation of compounds of pharmaceutical interest in a biological matrix for the purposes of quantitation. This chapter covers reversed-phase, ion-pair, hydrophilic interaction liquid chromatography (HILIC), and chiral HPLC. Other techniques such as normal phase and ion-exchange, with respect to quantitative bioanalysis, have become less popular in recent years and are therefore not covered in this chapter. There are two main reasons for this reduced popularity: mass spectrometry (with its need for volatile mobile phases) now dominates quantitative bioanalysis, and environmental considerations regarding solvent disposal are more pressing.