Financial social media refers to platforms where users discuss and share information related to financial markets, investments, and economic trends where users exchange ideas, seek advice, and stay updated on financial news. This second edition includes theoretical models, new methodologies, and empirical data, along with tests that reveal how online communication not only impacts stock returns, but also volatility, trading volume, and liquidity, as well as an investing firm's value and reputation. The book introduces what financial social media is and why it's important. It discusses who is more likely to post messages on financial social media and why while demonstrating how to measure financial social media activities using statistical approaches. Based on intuition, logic, and empirical evidence, the book explores the patterns of posting activities and argues that online talk does matter to investors. It also discusses trading strategies for both retail and institutional investors, and looks to the future in how the industry might change. It will be of interest to researchers of financial services, social media, behavioral finance, and risk management, alongside policymakers and practitioners.