Its simple really – there are only three:
One person takes responsibility for prioritizing what to work on; he is called the Product Owner (PO). In the wider perspective he takes responsibility for Business Value generated in the project and the return on investment (ROI).
The PO understands the domain of the customers and users and also takes responsibility for explaining this to the Team working on the deliverables. The PO often finds the right people from the outside for the Team to talk to in order to reach common understanding. The Team has exactly one point of reference as to “what we build” and “when”, that is the PO.
The PO operates most intensely in the strategic area between the domains with complex and complicated items and he plans the tactical Sprints together with the Team. The PO constantly works with the Product Backlog, improves explanations, gathers new ideas, acquires acceptance criteria, listens for signals from users, re-prioritizes etc.
A small team (3 to 9 individuals) take responsibility for producing the actual deliveries in the project; we call this the Development Team or in short – the Team. The Team is self-organizing, cross-functional and ideally has all the necessary skills to actually produce the deliverables as described in the Product Backlog.
Ideally, there are no dependencies on anybody or anything outside the Team so they can focus entirely on the Product Backlog. They are in the Team full-time and optimally co-located.
The authority to find the right solution, “how to build” the deliverables, rests with the Team. They have the necessary authority, resources and commitment to assume this responsibility. In dialogue with the Product Owner and based upon priority, the Team chooses the set of Product Backlog Items that they can commit to in the following Sprint. After this they are left to do the job in the Sprint. It is also the Team’s responsibility to make their progress and potential impediments visible to everybody.
The Team works with the Product Owner to raise the understanding of Product Backlog Items, such as finding acceptance criteria. The Team estimates the size of work associated with Product Backlog Items and helps the PO to decompose large PBIs.
One person takes responsibility for governing the Scrum process, implementing improvements, removing impediments and protecting the Team and the Product Owner. He is called the Scrum Master (SM). He is not the usual project manager or team leader handing out tasks to Team members; instead he is a true leader who serves the Team and the larger organization by clearing the road for the Team thereby improving the quality of work being done.
The Scrum Master is focused on achieving a spirit of constant improvement, so he has to be deeply convinced of the values of Scrum. Often he will work with the whole surrounding organization and explain why and how Scrum is used.
The Scrum Master adds value to the project by always observing and listening for weak signals, indicating either opportunity or potential danger. In a way he is the one who is most exposed to the complex domain, constantly living and breathing it, making sure that the entire Team doesn’t slip into mistakenly assumed simplicity, where this does not exist. He tries to create room in the Sprint – in time and space – for the Team to find and create solutions and get into flow; this is partly done by protecting the Team from the constant changes and interruptions from the surroundings.
The Scrum Master is like the coach of a sports team, like the conductor of the orchestra or like the sheepdog watching over the Sheep – at all times serving the Team and the Product Owner.