Research into the psychology of programming and the underpinnings of software complexity has been on-going for nearly 50 years. A wealth of quantitative complexity measures exist for code, but their relationships to the cognitive processes of the programmer are based largely on out-dated models of the brain and memory. More modern models of program comprehension exist, but are effectively qualitative in nature. In this talk, I will give an overview of the existing “cognitive” models of software complexity (past and present) while trying to motivate a research program towards developing a modern quantitative model based on a combination of Computer Science and Cognitive Science.