The vast majority of the conflicts in which British soldiers were involved in the period 1750-1815 took place abroad, bringing them into unprecedented contact with foreign cultures and manners. This encounter with ‘the other’ presented a wide range of challenges and dilemmas. These are more noticeable among those who decided to serve in foreign armies, applying in many cases know-how acquired in the British regular army, militia or/and volunteers forces. This chapter will examine some of the experiences of British soldiers who joined as volunteers the Spanish and French forces during the Napoleonic wars. It provides an overview of their motivations to fight under a foreign flag and makes an appraisal of the effects of their engagement on their national loyalties and identities as well as exploring cultural cross-fertilization. Relations with their compatriots in the British army, particularly with military leaders such as Sir John Moore and Lord Wellington, are also considered in order to provide a meaningful sidelight on the way the British authorities conducted the business of war.