This is a work of reference in two parts: part 1 is an itemized list of the contents of all the manuscript and printed sources of British keyboard music to c. 1660; part 2 is a thematic index, listed alphabetically by composer, of all the pieces contained in the sources. Each piece in the index is numbered and that number will also be found against its entry in the source list; thus each piece may be placed in the context of its origins. The book concludes with a computerized code of the musical incipits, so that it is possible to discover if any piece is included in any source. The index itself consists of the musical incipit, and a list of all the known sources, with folio numbers, deviant titles and ascriptions, and modern printed sources, if any.