The scrum of scrums is a technique to operate Scrum at scale, for multiple teams working on the same product, allowing them to discuss progress on their interdependencies, focusing on how to coordinate delivering software, especially on areas of overlap and integration.
Depending on the cadence (timing) of the scrum of scrums, the relevant daily scrum for each scrum team ends by designating one member as an ambassador to participate in the scrum of scrums with ambassadors from other teams. Depending on the context, the ambassadors may be technical contributors or each team's scrum master.
Rather than simply a progress update, the scrum of scrums should focus on how teams are collectively working to resolve, mitigate, or accept any risks, impediments, dependencies, and assumptions (RIDAs) that have been identified. The scrum of scrums tracks these RIDAs via a backlog of its own, such as a risk board (sometimes known as a ROAM board after the initials of resolved, owned, accepted, and mitigated), which typically leads to greater coordination and collaboration between teams.
What risks, impediments, dependencies, or assumptions has your team resolved since we last met?
What risks, impediments, dependencies, or assumptions will your team resolve before we meet again?
Are there any new risks, impediments, dependencies, or assumptions slowing your team down or getting in their way?
Are you about to introduce a new risk, impediment, dependency, or assumption that will get in another team's way?
One way to look at Scrum of Scrums is to say that it is a 'meta-scrum'. In large software projects where the product increments have to be shipped continusly 200 or 300 times a in a two week sprint, the master of scrum of scrums is responsible for making the trains runs on time. For scaling agile Scrum of Scrums is a great way to consider for your organisation.
A properly executed Scrum of Scrums is the minimum viable release team for products and product lines. It removes the waste introduced into many Scrum implementations by integration teams, release teams, and release management teams introduced by scaling frameworks that distort Scrum and make it less agile by increasing communication pathways. Ken Schwaber called this an Integration Scrum in his book on Enterprise Scrum.
For teams working on disparate projects or products that have no integration, the Scrum of Scrums is often used as a coordinating mechanism for the organization and may therefore meet less frequently.
Outside the Scrum of Scrums meeting, relevant individuals from the meeting volunteer to deal with eliminating operational impediments that are identified related to the release and deployment process. This is fractally equivalent to Scrum team members working together in a Sprint. For example, a Scrum of Scrums would have coordination mechanisms to deal with cross-team dependencies related to completion of epics required for release.
The role of management in a Scrum of Scrums is critical. They hold the Scrum of Scrums Master accountable for delivery. As a result the Scrum of Scrums Master is usually a more senior person, often at the Director of Engineering or higher level. The Scrum of Scrums is not the Enterprise Action Team (EAT - the management team that deals with company impediments). The Scrum of Scrums may refer company issues to the EAT, although the Scrum of Scrums deals directly with operational issues.