Philip Sidney, nephew of Robert Dudley, Earl of Leicester (and Elizabeth's favourite) has become for us, as for at least some of his contemporaries, the epitome of the Renaissance courtier. However he is a far more complex and ambiguous figure than that (see, for example, the excellent Stewart biography Sir Philip Sidney: A Double Life). This excellent collection, edited and introduced by Duncan-Jones, herself a renowned Sidneian, is a superb introduction to the contradictions of this immensely intelligent, cultured, and yet slippery man.
This contains his early writings, the eclogues from the 'Old' Arcadia, the full Defense of Poetry, the full Astrophil and Stella, prose excerpts from the 'new' Arcadia, and a handful of psalms. It is rounded off with a few of Sidney's own letters (about 15 or so) and a short appendix which includes some very (very) brief writings about Sidney's death.
Duncan-Jones is unobstrusive in her commentary but the serious student will need to consult other secondary literature. The letters are fascinating and this section could have been much longer as it's difficult to get an affordable copy of Sidney's correspondance.
However, the full Defense and Astrophil make this a bargain at the price. For the Sidney student, do also get the Oxford 'old' Arcadia with this (The Countess of Pembroke's Arcadia (The Old Arcadia) (Oxford World's Classics), as the intersections between the epic/pastoral romance of that,and the Petrarchan Astrophil really do need to be read in conjunction.