This single-movement setting of the Vesper psalm Laetatus sum was discovered by Michael Talbot in the spring of 2017 among the online collection of digitized scores of sacred music held by the SLUB in Dresden. Four works by Vivaldi deliberately misattributed to Baldassare Galuppi by the Venetian copyist Iseppo Baldan had already been uncovered in the previous decades, and it was during anexploratory examination of scores sharing a paper type and copyist (Baldan himself) with them that this fifth such work came to light. Vivaldi's single movement pieno settings (for choir alone without soloists) form an important subset of his sacred vocal music, and this new setting is the most elaborate and expansive of any of them. It features effective musical contrasts, and its many felicitous examples of word-painting show what a complete master of vocal composition he had become by the 1730s, the decade from which this setting clearly originates. As usual in Vivaldi's choral compositions the ever-changing relationship between the vocal and instrumental components constantly fascinates, as each in turn captures the listener's attention. This previously unknown Laetatus sum promises to become a much-performed work.