Robert Leslie Ellis's papers form a subset of the William Whewell papers and consist of his letters, notebooks, diaries, and writings. The Whewell papers are dispersed under various shelf marks in Additional Manuscripts and Wren classes O and R. Ellis's outgoing letters date from 1838 to 1859 and are housed as part of nine numbers in Add.MS.a, c, and R: Add.MS.a.58, Add.MS.a.68, Add.MS.a.79, Add.MS.a.81, Add.MS.a.203, Add.MS.a.222, Add.MS.c.67, Add.MS.c.88, and R.6.13. Letters received appear in 4 numbers in Add.MS.a and c: Add.MS.a.68, Add.MS.a.79, Add.MS.a.81, and Add.MS.c.67.
His diaries are dated 1827-1845 and are housed as part of Add.MS.c.67, Add.MS.a.82, Add.MS.a.218, and Add.MS.a.219. His notes and writings are housed as part of Add.MS.a.78, Add.MS.a.80, Add.MS.a.218, and Add.MS.a.219, Add.MS.a.220, Add.MS.a.221, Add.MS.a.222, Add.MS.a.223, and Add.MS.c.67. In addition, the Library also holds books owned by Leslie, including his copy of Whewell's On the Free Motion of Points 1832-1834, which has Ellis's notes on the endpapers.