This chapter reviews the literature on the lynchpin of expatriate success and of global families – the expatriate partner. To better understand the adjustment and well-being of expatriate partners, we focused on three major correlates that represented partner, expatriate, and family aspects. We first identified various personal (i.e., demographic, traits, knowledge/skills/abilities/others, and attitudes/cognitions), relational, organizational, and assignment factors that are associated with the expatriate partner’s adjustment. For expatriate influences on partner adjustment and well-being, we considered both personal and job/assignment factors. For the family variables, we looked at the perspectives of both the partner and the expatriate. Through our analysis of these detected associations, we observed three major themes: crossover occurrences from partners to expatriates, the relationship between the partner and family dynamics, and under-researched topics relevant to partner adjustment. For each theme, we discuss what we currently know (or don’t know), relevant theoretical perspectives to advance our knowledge in these areas, and suggestions for future research.