Today we are used to be identified and authenticated to various types of systems. We start very early in the morning unlocking our phones (if it has a PIN or other kind of security). We do it continually on websites, smartphones, doors, and so on. We are so used to be identified and authenticated that a lot of times we do not focus enough on the importance and the security of this critical process. In this chapter, we will focus on each of those and how to secure them.