People often recruit social resources to manage their emotions, a phenomenon known as interpersonal emotion regulation (IER). Despite its importance, IER's psychological structure remains poorly understood. We propose that two key dimensions describe IER: (a) individuals' tendency to pursue IER in response to emotional events, and (b) the efficacy with which they perceive IER improves their emotional lives. To probe these dimensions, we developed the Interpersonal Regulation Questionnaire (IRQ), a valid and reliable measure of individual differences in IER. Factor analyses of participants' responses confirmed tendency and efficacy as independent dimensions of IER (Study 1; N = 285), and demonstrated independence between how individuals engage with IER in response to negative, versus positive, emotion. In Study 2 (N = 347), we found that individuals high in IER tendency and efficacy are more emotionally expressive, empathetic, and socially connected. Two subsequent studies highlighted behavioral consequences of IER dimensions: people high in IER tendency sought out others more often following experimentally induced emotion (Study 3; N = 400), and individuals high in IER efficacy benefitted more from social support after real-world emotional events (Study 4; N = 787). Finally, a field study of social networks in freshman dormitories revealed that individuals high in IER tendency and efficacy developed more supportive relationships during the first year of college (Study 5; N = 193). These data (a) identify distinct dimensions underlying IER, (b) demonstrate that these dimensions can be stably measured and separated from related constructs, and (c) reveal their implications for relationships and well-being.