While looking at the strengths and weaknesses of contemporary approaches to parallelization this thesis suggests a form of parallelizing refactoring -- Invasive Interactive Parallelization -- that aims at addressing a number of weaker sides of contemporary methods. Our ultimate goal is to make the parallelization more user and developer friendly. While admitting that the approach adds complexity at certain levels, in particular, it can be said to reduce code understandability, we conclude that it provides a remedy for a number of problems found in contemporary methods. As the main contribution the thesis discusses the benefits we see with the approach, introduces a set of parallelization categories a typical parallelization consists of, and shows how the method can be realized with abstract syntax tree transformations. The thesis also presents a formal solution to the problem of automated round-trip software engineering in aspect-weaving systems.