More than a decade has passed since the emergence of major social media services such as Twitter and Facebook, and these services have attracted considerable attention from both practitioners and academics. The aim of this special issue is to re-examine the impact of social media in marketing. Consumer engagement behavior on social media was expected to enhance the marketing activities of firms in various areas, including advertising, customer support, and new product development. Along with these high expectations, the negative impacts of social media, such as backlashes against certain people or brands, spread of fake news and fake reviews have also affected firms and consumers. In this special issue, we shed light on various aspects of social media, including consumer enthusiasm and collective behavior, the resulting positive and negative bursts in social media, product reviews and their helpfulness, and usage patterns of social media by user segment.