Does a project need both (a scrum master and a project manager)---and what are the job responsibilities of each one ?

Scrum is an iterative and incremental agile software development methodology for managing product development. It defines "a flexible, holistic product development strategy where a development team works as a unit to reach a common goal", challenges assumptions of the "traditional, sequential approach" to product development, and enables teams to self-organize by encouraging physical co-location or close online collaboration of all team members, as well as daily face-to-face communication among all team members and disciplines in the project.

A project manager is a professional in the field of project management. Project managers can have the responsibility of the planning, execution and closing of any project, typically relating to construction industry, architecture, aerospace and defense, computer networking, telecommunications or software development.

It's suppose to run more professional and smooth, but I would say so in some projects.

Agree with the previous answers >>>>>>>>>>Thanks Mr. Yaqoup

It depends in the project kind. If it is an Agile software development project, for this case, a ScrumMaster is highly needed. The ScrumMaster serves as a facilitator for both the Product Owner and the team. It’s an arduous role that demands a distinct personality type to be successful—in large part because the ScrumMaster has no management authority and may never commit to work on behalf of the team. While the project manager serves the authority leader to execute the project and lead the team to produce the project deliverables.

Many short staffed teams or small organizations consider combining the role of Scrum Master (SM) and Product Owner (PO) into one person. Is it advisable? Have other people done it? What are the options? According to Mike Cohn, author of Agile Estimating and Planning, the Scrum Master is: ...responsible for making sure a Scrum team lives by the values and practices of Scrum. The ScrumMaster protects the team by making sure they do not overcommit themselves to what they can achieve during a sprint. The ScrumMaster facilitates the daily scrum and becomes responsible for removing any obstacles that are brought up by the team during those meetings. The ScrumMaster role is typically filled by a project manager or a technical team leader but can be anyone. In addition, the Scrum Master owns quality on behalf of the team. Whereas the Product Owner is: ... (typically someone from a Marketing role or a key user in internal development) prioritizes the Product Backlog. The Scrum Team looks at the prioritized Product Backlog and slices off the top priority items and commits to completing them during a sprint. These items become the Sprint Backlog. In return for their commitment to completing the selected tasks (which, by definition, are the most important to the product owner), the product owner commits that he or she will not throw new requirements at the team during the sprint. Requirements are allowed to change (and change is encouraged) but only outside the sprint. Once the team starts on a sprint it remains maniacally focused on the goal of that sprint. As Matt Gelbwaks pointed out, the Product owner is responsible for concepts and ideas (i.e. the backlog), while Scrum Master is responsible for execution and quality, so the Product Owner wants more features while Scrum Master is focusing on getting it done. Tomek Wlodarek explains that the different points of view are only half the problem. The other half is the time commitment: "In a corporate environment what I learnt is that a SM is a full time job for a team as big as5-6 people. ... the PO role for that team turned out to be60% -100% job." Dan Rawsthorne, Coach with Danube Technologies, wrote: I've done it, back in the day before I knew any better. ... I combined the PO, SM, and Lead Designer roles. In order to keep my team self-organized, I used to have skits in front of them: "on this hand... on the other hand... what should I do?" It worked out, but was very difficult, and I never want to do it again, and I don't want anybody else to try it either. Tom Mellor has also seen it work once, noting that it took a rather unique individual who is coaching full time now. Steve Eichert, had the most optimistic answer saying "Assuming a single person is able to fill both of these roles by not mixing and matching it seems feasible that they could be done by a single person if absolutely required.". However, even he recommends keeping them separate. Finally Ken Schwaber noted (in a CSM class) that experienced Scrum Master could pinch hit for the Product Owner until a proper one has been identified and trained.

Agree with the previous answers