Lockdowns during the COVID-19 pandemic increased the risk for loneliness. We tested whether nostalgia counteracts loneliness via rises in happiness. We conducted surveys in China (N=1,546), the U.S. (N=1,572), and the U.K. (N=603). Although feeling lonely was associated with unhappiness, it was also associated with nostalgia, which in turn conduced to increased happiness. We complemented these findings with three experiments testing MTurk workers (Study 4, N=209; Study 5, N=196; Study 6, N=190), where we manipulated nostalgia and assessed happiness. Nostalgia increased happiness immediately after the manipulation (Studies 4-6) and, following an induction booster, up to two days later (Studies 4-5). Nostalgia is a psychological resource that can be harnessed to raise happiness and help combat loneliness.