This study aimed to extend research on social cognitive theory (SCT) to explain consumers' engagement behavior in online brand communities (OBCs). Recently, marketers exploited OBCs, a nontraditional form of marketing communication, to reach their target consumers. In the current study, the SCT framework assumed that consumers' engagement behavior in OBCs was a socio-cognitive process that involves major cognitive factors such as self-efficacy and outcome expectation. In the proposed relationship, it was expected that engagement behavior in OBCs was a function of consumers' cognitive evaluation of self-efficacy, the positive (social and functional benefits) and negative (embarrassment) outcome expectations associated with engagement behavior. Overall, the results supported the proposed model. First, self-efficacy was shown to directly and indirectly influence consumers' engagement behaviors. Second, outcome expectations, especially functional outcome expectations, were found to be important predictors for engagement behaviors. Thus, the current results verified that SCT contributed to the existing OBCs research. Previous studies dominantly employed the social identification approach to explain consumers' engagement behavior in OBCs. However, the current dissertation acknowledged the limitations of social identification approach because it focused only on consumers' social motivations. The proposed model in the current research might be more useful than social identification approach, which is a dominant framework for OBCs research because the proposed model encompasses various important factors such as functional needs in engagement behavior. In addition, the current study also investigated the impact of engagement behaviors on consumer-brand relationship (CBR) and proposed two dimensions of CBR: social and functional dimension. CBR suggested that there are interpersonal relationship qualities between consumers and brands. Given that consumers in OBCs communicated about brands through engagement behavior and often became avid advocates of brands, CBR was relevant to the current context. The results showed that engagement behavior influenced CBR. Few studies showed that consumers' engagement behaviors in OBCs led to CBR development. Thus, this result provided the legitimacy for engagement behavior research in the context of OBCs because the current results showed the potential of OBCs as a marketing communication tool for CBR development.