The main role of a firewall in computer security is to monitor and control incoming and outgoing network traffic based on predetermined security rules. Firewalls act as a barrier between trusted internal networks and untrusted external sources, filtering out potentially harmful traffic and preventing unauthorized access to sensitive data. They can be hardware-based, software-based, or a combination of both. By blocking malicious activities and enforcing security policies, firewalls significantly enhance an organization’s overall security posture.