When received here, the Maxwell papers were mainly in a series of envelopes, in some confusion, and considerable work has been needed to arrange them on a systematic basis. No arrangement can be entirely satisfactory since much of the material is fragmentary and not always easy to date, and its relevance sometimes not obvious. The main body of the papers (section V) has been grouped under subject headings and arranged so far as possible chronologically under each heading. As to subject matter, wherever Maxwell himself gave a title to an item, this is quoted in inverted commas; failing this, the description is given by the cataloguer. As to dates, a precise date is normally quoted only if it occurs within the item. But as a good deal of the material can be linked to published work, reference to Maxwell's collected Scientific papers (SP) and the much more recent Scientific letters and papers (SLP) will in such cases provide a terminus ad quem for drafts or notes. In other cases, what is written on the back of the sheet may offer a terminus a quo, since Maxwell often used the back of answers to Cambridge examination papers, datable from the candidate's name, or of his own earlier articles, for drafts of new work. Most of the work on this collection was done in 1964-67, but thereafter pressure of other duties caused it to be laid aside, and the final stages have only been completed in the past twelve months.