The embassy conducted by Edward Montagu first earl of Sandwich to Madrid and Lisbon during the 1660s had three objectives. It was primarily intended to secure a commercial agreement that would improve trading rights for English merchants in Spanish ports. Related to this was the on-going English attempt to mediate a peace that would bring an end to the war between Spain and Portugal. The earl of Sandwich was also under more informal orders to try to secure the return of artworks that had belonged to Charles I and which had been acquired by the king of Spain at the time of the Commonwealth Sale. Using evidence from the extensive journal that the earl kept over the course of his embassies to Madrid and Lisbon, it is possible to reconstruct the process of negotiation that led to the successful outcome of his first two objectives. This material also contains information about his relations with the pre-eminent figures of the Spanish court. Sandwich appears to have been on particularly close terms with the count of Peñaranda with whom he exchanged visits and gifts. This friendship, however, served to compromise his political independence, and yielded no beneficial results in the efforts to secure the return of the Stuart paintings.