Clean code : a handbook of agile software craftsmanship Clean Code is divided into three parts. The first describes the principles patterns and practices of writing clean code. The second part consists of several case studies of increasing complexity. Each case study is an exercise in cleaning up codeof transforming a code base that has some problems into one that is sound and efficient. The third part is the payoff: a single chapter containing a list of heuristics and smells gathered while creating the case studies.