Golden Oldie: Republication of "The Redshift of Extragalactic Nebulae" by F. Zwicky, published online on 18 November 2008. The paper discusses the main characteristics of extragalactic nebulae and the methods used to study them, with a detailed examination of their redshift. Different theories explaining this phenomenon are briefly reviewed, and the significance of redshift for studying penetrating radiation is highlighted. The introduction notes that certain space objects, visible as fuzzy spots through small telescopes, were found to lie beyond the Milky Way with the help of modern telescopes. These nebulae, revealed by the Hundred-Inch-Telescope on Mount Wilson, are stellar systems similar to the Milky Way. They are homogeneously distributed in space and appear as individuals or in clusters. The paper aims to provide a brief account of their key characteristics and the methods used to determine them.Golden Oldie: Republication of "The Redshift of Extragalactic Nebulae" by F. Zwicky, published online on 18 November 2008. The paper discusses the main characteristics of extragalactic nebulae and the methods used to study them, with a detailed examination of their redshift. Different theories explaining this phenomenon are briefly reviewed, and the significance of redshift for studying penetrating radiation is highlighted. The introduction notes that certain space objects, visible as fuzzy spots through small telescopes, were found to lie beyond the Milky Way with the help of modern telescopes. These nebulae, revealed by the Hundred-Inch-Telescope on Mount Wilson, are stellar systems similar to the Milky Way. They are homogeneously distributed in space and appear as individuals or in clusters. The paper aims to provide a brief account of their key characteristics and the methods used to determine them.