Roland Bittleston, a researcher at the Perimeter Institute for Theoretical Physics, opens a two-part introduction to self-dual theories, a class of field theories, such as self-dual Yang-Mills and self-dual gravity, where the field strength equals its own dual. Recorded as part of the Prospects in Theoretical Physics summer school program, this first session lays out the basic definitions and motivations for studying these simplified theories, which strip away much of the complexity of full gauge and gravity theories while preserving features physicists care about, including integrability and connections to twistor methods. Bittleston builds the material from first principles, aimed at an audience of graduate students and early-career researchers attending the program, setting up the technical machinery that the second part of the primer will extend further. The talk runs just over an hour and keeps close to blackboard-style derivation rather than slides.