This book provides a comprehensive coverage of the state-of-the-art in understanding media popularity and trends in online social networks through social multimedia signals. With insights from the study of popularity and sharing patterns of online media, trend spread in social media, social network analysis for multimedia and visualizing diffusion of media in online social networks. In particular, the book will address the following important issues: Understanding social network phenomena from a signal processing point of view; The existence and popularity of multimedia as shared and social media, how content or origin of sharing activity can affect its spread and popularity; The network-signal duality principle, i.e., how the signal tells us key properties of information diffusion in networks; The social signal penetration hypothesis, i.e., how the popularity of media in one domain can affect the popularity of media in another. The book will help researchers, developers and business (advertising/marketing) individuals to comprehend the potential in exploring social multimedia signals collected from social network data quantitatively from a signal processing perspective.