Publisher Summary Liquid chromatography/mass spectrometry (LC/MS) is widely applied in biomedical and biochemical research and pharmaceutical product quality control. This chapter describes major developments in the application of LC/MS in environmental analysis, particularly, the determination of polar pesticides and related compounds, for three interfacing techniques: thermospray (TSP), particle beam (PB), and atmospheric pressure ionization ((API): electrospray (ESP) and atmospheric pressure chemical ionization (APCI)). The chapter focuses on phenylurea herbicides, triazines, carbamates, organophosphorus pesticides, chlorinated phenoxyacetic acids, and quaternary ammonium salts, among the vast number of pesticides. The chapter shows the potential of a variety of LC/MS techniques for the trace-level identification and/or quantification of analytes covering a wide polarity and volatility range. A major drawback of LC/TSP-MS is the limited structural information provided by the mass spectra. In the field of environmental analysis, use of LC/MS in routine laboratories still is somewhat limited, but the increasing interest for polar pesticides and industrial chemicals, and their more polar (bio)degradation products indicate that more widespread use for routine purposes can be expected in the near future.