Although quadrupole mass analyzers represent approximately 90% of all inductively coupled plasma mass spectrometry (ICP-MS) systems installed worldwide, limitations in their resolving power have led to the development of high-resolution spectrometers based on the double-focusing magnetic sector design. In this chapter, we take a detailed look at this very powerful mass separation device, which has found its niche in solving challenging application problems that require excellent detection capability, exceptional resolving power, and very high precision.