We organize the literature on triggers and functions of nostalgia by advancing a regulatory model in which the emotion serves as a homeostatic corrective (i.e., a process that establishes and maintains a relatively stable psychological equilibrium) that countervails the negative effects of psychological perturbations and adverse environmental conditions. We illustrate complementary approaches to testing this model as it applies to transient, or state-level, nostalgia and show how the model can be generalized to different levels of analysis, including chronic, or trait-level, nostalgia and collective nostalgia. We then formulate a proposal for future research inspired by recent developments in causal mediation analysis and conclude with a discussion of the model’s potential boundary conditions.