Recently HPLC-MS/MS has gained increasing popularity in clinical laboratories due to the advantages of the technology over other methods, while the capital cost for instruments has been decreased. HPLC-MS/MS provides high specificity and sensitivity for the simultaneous measurement of several drugs and/or their major metabolites in one single analytical run. In this book chromatographic methods published in the last decade are reviewed regarding their applicability to drug monitoring. HPLC methods for anti-cancer drugs, bronchodilators, cardiovascular drugs, antipsychotics, antibiotics, antiepileptic drugs, antidepressants, and immunosuppressants have been presented comprehensively regarding sample preparation and chromatographic separation. Supportive information has been included on HPLC analysis and sample preparation.