Project Management Body of Knowledge (PMBOK) describes the entire quantity of theory and learning that encompasses the practice of project management. These theories are dynamic, integrative processes that are in constant evolution as practice grows and changes. Similar to other disciplines, the content of the project management body of knowledge is defined, tested, and reformed by the individuals who utilize and foster increasing knowledge within the realm of project management.

The entire project management body of knowledge incorporates scientifically sound theories in project management along with novel theories and processes that are being tested and proven. The project management body of knowledge includes formal written frameworks of practice as well as informal and unwritten knowledge. Project management is itself a complete science and as a discipline is useful in a wide variety of domains such as software engineering, construction, architecture, and automotive utilizations. There are five process groups (or steps) and nine knowledge areas in project management. Each of the nine knowledge areas in itself contains the five process groups. Each knowledge area needs all five process groups in order to function. Every process in a project management plan becomes interrelated to at least one knowledge area and one process group.

The first version of the PMBOK was published in 1987, the second version in 1996, the third version in 2004, the fourth in 2008, and the fifth in 2013. Members of the PMI can download a digital copy of the PMBOK for free.