Open-source intelligence (OSINT) is the practice of gathering information from publicly available sources. The text describes how OSINT, initially used by military and intelligence agencies, is now crucial for cybersecurity. It details how organizations use OSINT to discover and analyze public-facing assets, identify potentially sensitive information, and improve their overall security posture. The text also lists numerous OSINT tools, outlining their functionalities and uses, emphasizing the importance of ethical and legal considerations when employing these techniques. Finally, it stresses the need to proactively address publicly accessible vulnerabilities to prevent exploitation by malicious actors.