The use of communication networks and the Internet has rocketed in the last years. From the traditional, wired settings to the wireless ones, connectivity is becoming almost ubiquitous in modern societies. Security concerns are critical, such as data forgery or tampering. In order to address these needs, security protocols have been proposed for each setting over the years. This chapter introduces the essential aspects of several representative protocols concerning authentication, remote connection, secure data exchange, and wireless protection for networks and Internet. Remarkably, basic notions on well-known protocols such as Kerberos are presented without entering into low-level details.