This dissertation investigates the impact of social interaction in the financial market. The focus of this defense is on understanding 1) how investment information is transmitted from one investor to another and 2) how social interaction between investors change their trading strategies. The first chapter of this dissertation finds that conversational norms shape the diffusion of investment information. The results in the second chapter show that investors are more likely to drastically adjust their investment strategies when other investor’s current buying (selling) strategies and past performance are consistent.