The differences between Old-Roman, Ambrosian, Aquileian, Gallican, and Hispanic chant, and their interconnections with each other and the Gregorian chant occupied Michel Huglo in his early career, although he returned to these questions in the 1980s and 1990s. The present volume, the second in the set of four to be published in the Variorum series, brings all this work together. Huglo’s 1954 article, the first to describe the sources for Old Roman chant, recognized as distinct from Gregorian chant, is of primary significance for the historiography of Western plainchant, because it opened the debate on the relationship between Old Roman and Gregorian chant. The final section presents articles on the Latin version of the Akathistos hymn and on Byzantine chants translated into Latin that became part of the Western plainchant repertory. Les differences entre les repertoires Vieux-romain, Ambrosien, Aquileien, Gallican et Hispanique, leurs influences reciproques et leurs relations avec le chant gregorien ont occupe Michel Huglo au debut de sa carriere: il revint sur ces questions dans les annees 1980 et 1990. Ce volume, le deuxieme d'une serie de quatre dans la collection Variorum, reunit toutes ces etudes. L'article de 1954 de Michel Huglo sur les sources du chant Vieux-romain, considere comme distinct du gregorien, est de premiere importance pour l'historiographie du plain-chant occidental, car il a ouvert les debats sur le rapport entre Vieux-romain et gregorien. Les articles sur la version latine de l'Hymne Acathiste et sur les pieces de chant byzantin traduites en latin dans les repertoires occidentaux du plain-chant achevent ce volume.