This chapter discusses one of the most important types of cybersecurity training platforms in terms of public perception, namely the Capture The Flag (CTF) platforms. First, we examine the two main types of CTF content, which are Jeopardy style and attack-defend, and discuss their respective advantages and disadvantages. Then we present in detail two categories of CTF platforms, online and open-source ones, with several representative examples of actual platforms in each category. The examples we discuss are classified in Jeopardy-style platforms and hybrid ones, which also support attack-defend style competitions. The main characteristics of each platform are then analyzed in a comparative manner for each platform category. Finally, we discuss some important aspects that should be considered in relation with CTF platforms, such as their potential disadvantages, security issues, etc.