The popularity of online social networks has rapidly increased over the last decade. While serving its primary purpose of connecting people, social networks also play a major role in successfully connecting marketers with customers, famous people with their supporters, need-help people with willing-help people. The success of online social networks mainly relies on the information that the messages carry as well as the spread speed in social networks. This book aims at modeling message diffusion, extracting and representing information and knowledge from messages in social networks.