The Countess of Pembroke's Arcadia, also known simply as the Arcadia, is a long prose pastoral romance by Sir Philip Sidney written towards the end of the 16th century. Having finished one version of his text, Sidney later significantly expanded and revised his work. Scholars today often refer to these two major versions as the Old Arcadia and the New Arcadia. The Arcadia is Sidney's most ambitious literary work by far, and as significant in its own way as his sonnets.

Sir Philip Sidney was an English poet, courtier, scholar and soldier who is remembered as one of the most prominent figures of the Elizabethan age. His works include a sonnet sequence, Astrophel and Stella, a treatise, The Defence of Poesy and a pastoral romance, The Countess of Pembroke's Arcadia.