Although social media usage in business markets continues to grow, managers still struggle with designing popular brand message posts. This research investigates the key factors that contribute to Facebook brand content popularity metrics (i.e., number of likes and comments) for Fortune 500 companies' brand posts in business-to-business (B2B) versus business-to-consumer (B2C) markets. Building on psychological motivation theory, the authors examine key differences in B2B and B2C social media message strategies in terms of branding, message appeals, selling, and information search. Using Bayesian models, they find noteworthy differences in the propensity of viewers to popularize brand posts. Specifically, the results indicate that the inclusion of corporate brand names, functional and emotional appeals, and information search cues increases the popularity of B2B messages compared with B2C messages. Moreover, viewers of B2B content demonstrate a higher message liking rate but a lower message commenting rate than viewers of B2C content.