The definition of high resolution in IR spectroscopy has been changing with time. In this article, the limit of high resolution is defined as 0.1 cm-1. This is the full width at half height (FWHH) of the line; in other terms the higher the resolution, the smaller the FWHH. In history, grating and even prism spectrometers, which have a lower resolution than 0.1 cm-1, have also been regarded as high-resolution instruments, but the development of spectroscopic instrumentation has pushed the limit of high resolution towards smaller FWHH. Nowadays, high-resolution IR spectra are generally recorded by Fourier-transform IR (FT-IR) spectrometers, or by laser spectrometers. This article focuses on the last two types of spectrometers.