The collection includes:
- English and Italian madrigal part-books
- polyphonic manuscript part-books, from c. 1600, with sacred and secular works of English and Continental composers
- the most important source for Purcell's Dido and Aeneas
- Adrian Batten's organbook
- autograph manuscripts of Blow, Boyce, Burney, Wesley and other English composers
- Handel's annotated score of Messiah used at the 1742 Dublin premire (MSS Tenbury 346-7)
- important sources of early Italian monody
- a copy of Beethoven's Seventh Symphony with many corrections by the composer
- autograph manuscripts of J.C. Bach, Cimarosa and Galuppi
- manuscript Italian operas, especially of the 18th century
- sacred works from the 17th-19th centuries
- autograph manuscripts of Ouseley's own compositions
- a few autograph letters of English musicians, [ca. 1800].