The far-infrared, defined herein as the spectral region between 15 and 100 micrometers, is a virtually unobserved component of the infrared emission spectrum of the Earth and its atmosphere. The radiative balance of the troposphere is influenced strongly by radiative cooling associated with emission by water vapor at far-infrared wavelengths extending out beyond 50 micrometers. Up to half of the outgoing longwave radiation from the Earth occurs in the far-infrared, depending on atmospheric and surface conditions, and up to half of the natural greenhouse effect occurs in the far-infrared. The distribution of water vapor and associated far-IR radiative forcings and feedbacks are well recognized as major uncertainties in understanding and predicting future climate. Despite this fundamental importance, far-infrared emission (spectra or band-integrated) has rarely been directly measured from space, airborne, or ground-based platforms. Current and planned operational and research satellites observe the mid-infrared only to about 15.4 micrometers. NASA has recently selected the Far-Infrared Spectroscopy of the Troposphere (FIRST) project for development under its Instrument Incubator Program. In this talk we will review the importance of the far-infrared, discuss the advanced technology that will enable routine space-based observations of the far-infrared, and highlight the role of far-infrared spectral observations in the overall climate observing system of the future.