As a writer, Robert Sidney, Viscount Lisle and Earl of Leicester, Governor of Flushing, brother of Sir Philip Sidney, is known for a series of poems written probably for his wife Barbara. The remarkable autograph manuscript of these poems (British Library, Add. MS 58435) did not effectively come to light until the 1970s and was published in full in 1981 and 1984.
Sidney also compiled at least four large systematically arranged commonplace books, on political and other subjects (SiR 61-64), written perhaps largely during the years of his virtual isolation in Flushing.
Otherwise, as with so many public figures, his principal outlay of manuscripts was the numerous letters he wrote in his rugged cursive italic — a characteristic script for which, in one of his several letters of advice to Robert, his brother Philip had upbraided him years earlier (‘...I would by the way your worship would learne a better hand, yow write worse than I, and I write evell enough...’, 18 October 1580). Considerable numbers of letters by Robert Sidney are in repositories including the Sidney family archive of the Viscount De L'Isle at the Centre for Kentish Studies, Maidstone; the library of the Marquess of Salisbury, Hatfield House; the British Library; the National Archives, Kew; Lambeth Palace; Sheffield Archives; the Huntington; Yale; and the General Archives, Brussels. Facsimile examples of his letter-writing include those in Croft's edition of The Poems (1984), p. 75; in W. Schrickx, ‘Letters in Belgian Archives of Two English Poets, Robert Sidney and Henry Wotton’, Revue des Langues Vivantes, 20 (1974), 483-8 (p. 489); in Sotheby's sale catalogue The Trumbull Papers (14 December 1989), lot 34; and in Germaine Warkentin and Noel Kinnamon, ‘Robert Sidney and the Italic Hand’, Sidney Journal, 25 (2007), 83-93 (pp. 91 and 93, with a probably scribal letter illustrated on p. 92).
Books from Sidney's Library
Many books from Sidney's library, kept chiefly at Penshurst, have been widely scattered in subsequent sales, though a 219-leaf folio catalogue at Penshurst, made by the Sidney family secretary Gilbert Spencer, bears witness to the library there at least in the time of Robert Sidney's son, the second Earl of Leicester. For discussions of this library, with references to various of Robert Sidney's books that have come to light hitherto, see especially Germaine Warkentin, ‘The World and the Book at Penshurst: The Second Earl of Leicester (1595-1677) and his Library’, The Library, 6th Ser. 20 (1998), 325-46; her ‘Robert Sidney and His Books’, Sidney Journal, 25 (2007), 31-42; and Joel Davis, ‘Robert Sidney's Marginal Comments on Tacitus and the English Campaigns in the Low Countries’, Sidney Journal, 24 (2006), 1-19.
In addition, examples of continental manuscript libri amicorum have been discovered bearing signed inscriptions by both Philip and Robert Sidney: see SiR 65-66.