Robert Ignatius Letellier has specialized in the music and literature of the Romantic Period. He has studied the work of Giacomo Meyerbeer (a four-volume English edition of his diaries, a collection of critical and biographical studies, a guide to research, two readings of the operas, as well as compiling and introducing editions of the complete libretti and non-operatic texts, and a selection of manuscripts facsimiles). He has also written on the ballets of Ludwig Minkus, compiled a series of scores on the Romantic Ballet, a sourcebook on the French opéra-comique, a study of Daniel-François-Esprit Auber, and edited anthologies of his overtures, ballet music, and a series of his operatic vocal scores.