The distinguishing characteristic of code-based testing methods is that, as the name implies, they are all based on the source code of the program tested, and not on the specification. Because of this absolute basis, code-based testing methods are very amenable to rigorous definitions, mathematical analysis, and useful measurement. In this chapter, we examine the two most common forms of path testing. The technology behind these has been available since the mid-1970s, and the originators of these methods now have companies that market very successful tools that implement the techniques. Both techniques start with the program graph; we repeat the improved definition from Chapter 4 here.