English-language titles are capitalized headline-style (see below).
The following general guidelines are adapted and summarized from ModLangAssoc, 3.7.1–9; CMS16, 8.154–97 (English capitalization); and CMS16, chapter 11 (foreign-language capitalization):
In English: Capitalize (1) the first word of a sentence; (2) the subject pronoun “I”; (3) the names of persons; (4) names of months and days of the week; (5) personal titles that immediately precede a person’s name, in which case the title becomes part of the name (Professor of Musicology Peter Burkholder; President Abraham Lincoln), but not when the title is used separately (Burkholder is a professor of musicology; Lincoln was the sixteenth president); (6) other proper nouns, including names of organizations, and most adjectives derived from proper nouns.
In titles & subtitles: Capitalize first and last words, and all principal words (nouns, pronouns, verbs, adjectives, adverbs, subordinating conjunctions), including those that follow hyphens in compound terms (i.e., headline style). Do not capitalize articles (a, an, the), prepositions (in, of, to, etc.), coordinating conjunctions (and, but, for, etc.), the “to” in infinitives (“to be”). Exception: articles are commonly capitalized when immediately preceding, and part of, the name of a popular-musical group: The Ramones, The Byrds.
In French, Italian, Spanish, Portuguese, Russian (Cyrillic or roman alphabet): Capitalize as in English, with the following exceptions. Except at the beginning of a sentence, Do not capitalize (1) the subject pronoun in the language for “I”; (2) names of months and days (exception: names of months are capitalized in Portugal); (3) adjectives derived from proper nouns; (4) titles preceding personal names (the duc de Bourbon, el dottor Bartolo; exception: "Don" is capitalized in Italian, but not "dònna"; thus Don Giovanni, but dònna Anna); (5) names of languages and nationalities; (6) words meaning “street,” “square,” etc., in most place names (exception: these are capitalized in Brazil).
In titles & subtitles: Capitalize only the first word (including if it is an article), and other words that are normally capitalized (i.e., sentence style: “La musique et l’amour”).
Examples: Poulenc's Les mamelles de Tirésias; Puccini's La fanciulla del West; Ravel's L'heure espagnole; Ponce's Tema variado y final; Petrov's Kontsertino-buff. In French, do not use the alternative style in which the first substantive (noun or noun form) and any preceding article are both capitalized (“La Musique et l’amour”), as used in some journals, such as the French Review.
In German: Capitalize all nouns (including other parts of speech when used as nouns), and the pronoun Sie (you), its possessive Ihr (your), and their inflected forms. Note: German nouns that appear in MW11 or Webster's 3d are considered to be Anglicized, and are not capitalized or italicized in running text; thus lieder, not Lieder; gesellschaft, not Gesellschaft. Do not capitalize (1) the subject pronoun ich (I); (2) the names of languages and days of the week when used as adjectives, adverbs, or complements of prepositions; and (3) adjectives and adverbs formed from proper nouns, except when the proper nouns are names of persons, and the adjectives and adverbs refer to the persons’ works or deeds.
In titles & subtitles: Capitalize the first word, and all words normally capitalized in running text. Examples: R. Strauss, Die schweigesame Frau; Emanuel Bach, Clavier-Sonaten und freye Fantasien nebst einigen Rondos; Schoenberg, Einst hat vor deines Vaters Haus.
"American Music since 1910" (lowercase "since"; in CMS16, 8.157)
A Guide to Composing Music as Good as Mozart's
Institutions (CMS16, 8.57)
the University of Louisville; the university
the Cleveland Orchestra; the orchestra
the Library of Congress; the library
the New England Conservatory; the conservatory
head of the Special Collections Department; head of the department
Calvin Elliker was head of the Music Library and assistant professor of musicology at the University of Michigan (CMS16, 8.18).
Bibliothèque nationale de France; le Conservatoire de musique (CMS16, 11.29: for organizations & institutions, the first substantive is capitalized, but not the preceding article). Note that foreign-language proper nouns are not italicized.
Cultural Periods and Styles
Middle Ages (but medieval era), Gregorian chant, Gothic, antiquity, Renaissance, baroque, classical, classicism, colonial, romantic, romanticism, impressionism, neoclassicism, modernism, postmodernism, Viennese school (CMS16, 8.70–73, 8.78; and MW11. Holoman, 2.37, on the other hand, recommends capitalizing all commonly used periods of music history).
For Latin titles of modern journals, series, etc., follow CMS16, 11.59 ("Renaissance and modern works or works in English with Latin titles are usually capitalized in the English fashion"). Examples:
Acta Musicologica (not Acta musicologica); the series Musica Britannica (not Musica britannica).