In this part of the course, you'll learn about programming languages and controllers that make this programmability possible. We will focus on one language in particular, Pyretic, which is from the Frenetic family of languages. We will also look at a runtime and northbound API called Resonance, which allows network programmers to write policies that respond to changing network conditions (e.g., security events, shifts in peak vs. off-peak time, traffic fluctuations or link failures).