Over the past three decades it has been amply demonstrated that high pressure is a powerful tool for understanding the molecular and electronic properties of matter. In this review we outline applications of interest to physical chemists. After a brief introduction we discuss a series of experiments under the headings Fluids and Solids. Under the rubric fluids we mention a series of experiments which relate molecular properties to bulk properties. Then we discuss the use of pressure in establishing the physical and chemical dynamic properties of fluids and in relating to theories of these phenomena. We mention also experiments in biophysical chemistry, especially protein structure, and some recent electrochemical experiments. In the area of solids we mention the characterization of molecular interactions in crystals, polymers and glasses, and the relative importance of molecular, unit cell and site symmetry on such interactions. We discuss the testing of a wide variety of theories where pressure has performed a unique function. We discuss a series of molecular rearrangements in the solid state and establish some rules governing solid state chemistry. Finally we discuss the role of pressure in establishing the properties of phosphors, quantum well lasers and superconducting materials.