As you begin to use Kali Linux for increasingly sensitive and higher-profile work, you will likely need to take the security of your installation more seriously. In this chapter, we will first discuss security policies, highlighting various points to consider when defining such a policy, and outlining some of the threats to your system and to you as a security professional. We will also discuss security measures for laptop and desktop systems and focus on firewalls and packet filtering. Finally, we will discuss monitoring tools and strategies and show you how to best implement them to detect potential threats to your system.