This paper investigates the role of social networks in information diffusion through a large-scale field experiment on Facebook. The study randomizes exposure to signals about friends' sharing behavior among 253 million users, revealing that exposure significantly increases the likelihood and speed of information sharing. It also examines the relative role of strong and weak ties in information propagation, finding that although strong ties are individually more influential, weak ties are more abundant and responsible for the spread of novel information. This suggests that weak ties may play a more dominant role in online information diffusion than previously believed. The study shows that exposure to content on the Facebook feed increases the probability of sharing, and that the effect is more pronounced when fewer friends are sharing. The results indicate that weak ties are more influential in spreading information that would otherwise not be shared, and that the majority of influence in the network comes from weak ties. The study also highlights the challenges of distinguishing between social influence and homophily in observational data, and emphasizes the importance of controlled experiments in understanding the causal effects of social networks on information diffusion. The findings have implications for understanding how information spreads in online environments and the role of social networks in shaping behavior.This paper investigates the role of social networks in information diffusion through a large-scale field experiment on Facebook. The study randomizes exposure to signals about friends' sharing behavior among 253 million users, revealing that exposure significantly increases the likelihood and speed of information sharing. It also examines the relative role of strong and weak ties in information propagation, finding that although strong ties are individually more influential, weak ties are more abundant and responsible for the spread of novel information. This suggests that weak ties may play a more dominant role in online information diffusion than previously believed. The study shows that exposure to content on the Facebook feed increases the probability of sharing, and that the effect is more pronounced when fewer friends are sharing. The results indicate that weak ties are more influential in spreading information that would otherwise not be shared, and that the majority of influence in the network comes from weak ties. The study also highlights the challenges of distinguishing between social influence and homophily in observational data, and emphasizes the importance of controlled experiments in understanding the causal effects of social networks on information diffusion. The findings have implications for understanding how information spreads in online environments and the role of social networks in shaping behavior.