We examined the longitudinal relation between behavioral inhibition (BI) and social anxiety symptoms and behavior and the mediating role of emotion regulation (ER). Moreover, we investigated the influence of parenting behavior on the development of ER strategies. Participants were 291 children (135 male) followed longitudinally from 2 to 13 years. Mothers were predominantly well educated and non-Hispanic Caucasian. Children were screened for BI using maternal report and observational measures (ages 2 and 3), parenting behavior was observed while children and their mothers participated in a fear-eliciting task (age 3), ER strategies were observed while children completed a disappointment task (age 5), and socially anxious behavior was measured via multimethod assessment at 10 and 13 years. Children who exhibited high BI in early childhood exhibited more socially anxious behavior across ages 10 and 13, and there was a significant indirect effect of BI on socially anxious behavior through ER strategies. Children who were high in BI demonstrated less engaged ER strategies during the disappointment task, which in turn predicted more socially anxious behavior. Furthermore, parenting behavior moderated the pathway linking early BI and ER strategies to social anxiety outcomes such that children who exhibited high BI and who received more affectionate/oversolicitous behavior from their mother displayed less engaged ER strategies and more socially anxious behavior than children low in BI or low in oversolicitous parenting behaviors. These findings expand on our understanding of the role that ER strategies and parenting play in the developmental pathway linking early BI to future social anxiety outcomes. (PsycInfo Database Record (c) 2021 APA, all rights reserved).