This paper discusses the correction of astronomical data for the effects of Galactic interstellar extinction, which varies with wavelength and spatial location. The main features of extinction from the infrared (IR) through the ultraviolet (UV) are reviewed, along with spatial variations in extinction properties. The paper highlights the wide range of extinction properties found in the Galaxy, particularly in the UV, and notes that while there are some general correlations between extinction curve shape and interstellar environment, the wavelength dependence of extinction is not fully understood. The paper presents several strategies for dereddening data, along with estimates of the uncertainties inherent in each method. It also presents a new derivation of the wavelength dependence of an average Galactic extinction curve from the IR through the UV, along with a new estimate of how this extinction law varies with the parameter R ≡ A(V)/E(B-V). These curves represent the true monochromatic wavelength dependence of extinction and are suitable for dereddening IR–UV spectrophotometric data of any resolution and can be used to derive extinction relations for any photometry system. The paper also discusses the importance of accurately correcting for extinction in order to obtain accurate energy distributions and the challenges posed by spatial variations in extinction. It concludes that while there is some order in the wide range of extinction curves, the correction of energy distributions for extinction remains a complex task. The paper also addresses the use of R-dependent extinction curves and the importance of using accurate extinction curves for dereddening. The paper provides a detailed derivation of the R-dependent IR-through-UV extinction curve, which can be used to correct for extinction in astronomical data. The paper also discusses the importance of using synthetic photometry to derive accurate extinction curves and the challenges posed by the limited availability of high-quality extinction data. The paper concludes that the use of R-dependent extinction curves is the best approach for correcting for extinction in astronomical data.This paper discusses the correction of astronomical data for the effects of Galactic interstellar extinction, which varies with wavelength and spatial location. The main features of extinction from the infrared (IR) through the ultraviolet (UV) are reviewed, along with spatial variations in extinction properties. The paper highlights the wide range of extinction properties found in the Galaxy, particularly in the UV, and notes that while there are some general correlations between extinction curve shape and interstellar environment, the wavelength dependence of extinction is not fully understood. The paper presents several strategies for dereddening data, along with estimates of the uncertainties inherent in each method. It also presents a new derivation of the wavelength dependence of an average Galactic extinction curve from the IR through the UV, along with a new estimate of how this extinction law varies with the parameter R ≡ A(V)/E(B-V). These curves represent the true monochromatic wavelength dependence of extinction and are suitable for dereddening IR–UV spectrophotometric data of any resolution and can be used to derive extinction relations for any photometry system. The paper also discusses the importance of accurately correcting for extinction in order to obtain accurate energy distributions and the challenges posed by spatial variations in extinction. It concludes that while there is some order in the wide range of extinction curves, the correction of energy distributions for extinction remains a complex task. The paper also addresses the use of R-dependent extinction curves and the importance of using accurate extinction curves for dereddening. The paper provides a detailed derivation of the R-dependent IR-through-UV extinction curve, which can be used to correct for extinction in astronomical data. The paper also discusses the importance of using synthetic photometry to derive accurate extinction curves and the challenges posed by the limited availability of high-quality extinction data. The paper concludes that the use of R-dependent extinction curves is the best approach for correcting for extinction in astronomical data.