This special issue of Plainsong and Medieval Music honours the memory of Michel Huglo (1921–2012) with four articles that resulted from two sessions of papers held on 11 May 2013 at the 48th International Congress on Medieval Studies at the University of Western Michigan. Titled ‘Chant and Liturgy: Papers in Memory of Michel Huglo’, the sessions were organised by Anna Grau, Cathy Elias and Daniel DiCenso, with papers given by Terence Bailey, Frank Lawrence, Rebecca Maloy (in collaboration with Emma Hornby), William P. Mahrt, Nils Holger Petersen and Michael Norton. Also included is a bibliography of Michel Huglo's articles and unpublished papers to 2012, complementing earlier bibliographies. Obituaries are also cited. Each article in this volume advances research on subjects that occupied Michel Huglo fully at different times in his life.

Terence Bailey has for most of his career researched and edited the chant of the Ambrosian rite, the rite dating from Late Antiquity of the cathedral of Milan and churches of that region. Here Bailey provides a comprehensive study of responsories with a mise-à-jour of scholarship and consideration of repertory, function, text and music, and performance.

Michel Huglo's interest in the Ambrosian rite began while he was among the monks of the Abbey of Saint-Pierre of Solesmes preparing the edition of the Graduel Romain to which he contributed volume 2: Les Sources. His early articles on Ambrosian psalmody and melodiae (1951), the Ambrosian hymn cycle taken over by the Cistercians (1952), and the twelve antiphons, some of them Ambrosian, for the breaking of the bread at Mass (1955) were followed by the fundamental Fonti e paleografia del canto ambrosiano (Milan, 1956), prepared with Luigi Agustoni, Eugène Cardine and Ernesto Moneta Caglio, which contains the first comprehensive list of the sources of this rite. Articles on the annuncio pasquale (1957) and an Ambrosian antiphon disseminated outside Milan (1959) were both completed at Solesmes. Thanks to an invitation from Thomas Forrest Kelly to the 2009 conference ‘Ambrosiana at Harvard’, Huglo returned to the topic of Ambrosian psalmody with an article (2010) including a comparison of the psalter of St Germain of Paris, BnF latin 11947 with the Ambrosian antiphoner. The great interest of the Ambrosian rite for Huglo was that its chant was unaffected by the Western system of eight tones, the subject of Huglo's Les Tonaires (1971) and of Bailey's editions of intonation formulas (1974), De modis musicis (1977–8), and the Commemoratio brevis (1979), as well as some of their later publications.

William P. Mahrt here reconstructs the most important processions held at Salisbury Cathedral, whose rite was widely adopted across England and remained in use until the reforms of the sixteenth century, a topic related to that of two earlier articles (2010, 2011). The processions following Christmas on December 26, 27 and 28, which were established during the initial phase of the cathedral's contruction, include prosas otherwise rare in the Sarum rite.

Michel Huglo's interest in processions was inspired by François Lesure, who recruited him as chercheur of the Centre nationale de la recherche scientifique (CNRS) in Paris in 1962.Footnote ¹ After Les Tonaires, Huglo's dissertation, was completed, at the suggestion of Lesure, Huglo prepared five RISM volumes describing more than 1,500 manuscripts: three on music theory manuscripts, two in collaboration with Christian Meyer and Nancy Phillips respectively, and two more on manuscript processionals (1999, 2004). These catalogues, which followed Huglo's earlier list of sources of Old Roman chant (1954) and Les Sources (1957) required Huglo's consultation of the majority of the manuscripts in situ in countless European and American libraries, most visited on ‘missions’ for the CNRS. All these volumes benefitted from his extensive correspondence with scholars around the world, greatly facilitated with the arrival of email, and from his habit to write every day with monastic regularity, whether at a desk, in a train station or airport, or on a train.

Emma Hornby and Rebecca Maloy continue their study of Old Hispanic chant, which has intrigued scholars not only as the music of a distinct and early Christian rite, but also because its neumatic notation cannot be transcribed with any certainty except for isolated chants that slipped through the major reform of the late eleventh century. Here, Hornby and Maloy first analyse the cadences of sacrificia (Old Hispanic offertories) and then 700 intonations across all genres of Old Hispanic chant in light of the earlier taxonomy and geography of Old Hispanic responsory verses by Don Randel. They recognise Randel's dialects but also common points between them and idiosyncratic manuscripts reflecting decisions of cantors.

Old Hispanic chant, like Ambrosian chant, interested Michel Huglo at Solesmes and again after his retirement. His very first article, published in 1949, concerned an Old Hispanic hymn for the Cross. Huglo's interest in Hispanic chant was then revived with studies on the penetration of Aquitanian manuscripts in Spain (1985) and the Codex Calixtinus (1989); in the latter, he observed the identical date assigned to the feast of the Dedication of the churches of Vezelay and Santiago da Compostela, at the beginning and end of the pilgrimage route. Yet Huglo's true Iberian calling came in 1991, when he came across a full-page diagram representing musical intervals in Lindsay's 1911 edition of Isidore's Etymologiae in the stacks of Bobst Library at New York University. This led to studies not just of the Etymologiae and the later Liber glossarum derived from it, but also of the entire tradition of musical diagrams that evolved from the lambda diagram representing Plato's ‘Soul of the World’, which was transmitted in manuscripts of the Timaeus, particularly in Calcidius's translation. Huglo's research on the Isidore diagram was conducted during his year as a visiting Mellon professor at the Institute of Advanced Studies in Princeton in 1990/1, and was informed by manuscript study during travel from 15 to 24 March 1991 to Madrid, Ávila, Salamanca, Silos and Las Huelgas. There followed articles on Old Spanish psalmody of 1992 and 1993, and on Isidore of Seville and the diagrams (1992, 1994, 1998, 2001, 2003, 2007). In 2009 he wrote on the prologues to the Leόn Antiphoner, and in 2011 on the chant from the Book of Revelations in the same manuscript. His very last article, ‘Musica ex numeris’, now in press, is a summa of his work on Platonic numbers and diagrams of music, and concerns the scales derived from the tetraktys, 1 2 3 4, and the number series 6 8 9 12.

Michael Norton's study concerns two early Austrian manuscripts, Graz UB 807 and Vienna ÖNB 13314, that have defied the normal tests for localisation, the latter a subject to which Michel Huglo contributed scholarship and thus prompted further studies. Norton here examines the antiphons for Rogations in both manuscripts, the descriptions of the Triduum sacrum in the sacramentary concluding the Vienna manuscript, and the problematic date of Dedication in Graz 807. Confirming the manuscripts’ association with Klosterneuburg, he argues that they had been kept together in the twelfth century in Seckau.

Michel Huglo's own interest in Klosterneuburg came not only from his cataloguing of the gradual Graz 807 in Les Sources and of manuscripts for RISM, but also, and especially, from the spring semester of 1990, when he taught two seminars at the University of Vienna at the invitation of Walter Pass, the first a survey of medieval music theory, and the second on the manuscript fragments of Austrian monasteries. The students in the second seminar made weekly excursions to work in monastery libraries throughout Austria, including Klosterneuburg. Thus, at the retirement of Janka Szendrei, Huglo immediately thought of Graz 807, once proposed as having a notation that was a predecessor of Hungarian notation, and prepared a study of that manuscript (2008), which was soon followed by new scholarship by Robert Klugseder (2008) and others on Klosterneuburg. The meeting in Vienna in 2011 was Michel Huglo's last IMS Cantus Planus conference, an opportunity he particularly enjoyed, despite the heat, for the chance to meet and share his learning with younger generations.

For his contributions to our understanding of medieval music, Michel Huglo was awarded the silver medal of the CNRS in 1987, the doctor of humane letters honoris causa from the University of Chicago in 1991, and was selected Corresponding Member of the AMS (1997), Honorary Member of the International Musicological Society (2007) and Fellow of the Medieval Academy of America (2008). He founded the musicology section of the Institut de recherche et d'histoire des textes, and was a vice-president of both the Henry Bradshaw Society and the Plainsong and Medieval Music Society.