This study examines the idea that youth's perceptions of their political interactions with important others are influenced by their own political interest to a greater extent than the perceived political interactions that influence youth's political interest. Hence, it was proposed that youth's perceptions of important others' (parents', teachers', friends') political views, political interest, political influence, and support, as well as of being susceptible to others' political communication, are all affected by their own political interest. Community samples of 908 13-year-olds and 869 16-year-olds were followed over 1 year. Latent change models supported the idea that youth's political interest significantly affected their perceptions of important others' political views, influence, and support over time in both cohorts. In 11 out of 12 longitudinal analyses, youth's political interest strongly affected perceptions of their political interactions with others, but none of the 12 analyses showed that the perceptions of political interactions with others strongly predicted a change in youth's political interest. These results suggest that the political interest of young people is an input in their political development, making politically interested youth active agents in their political interactions with their important others.