Difference between scrum master and senior scrum master

It is worth distinguishing between roles and job titles.

Scrum has only three roles: Scrum Master, Product Owner and development team member.

If you were doing Scrum, it would be nonsensical to have a role of Senior Scrum Master. This is because by defining a new role you are no longer doing Scrum.

However, there is no reason why an organisation should not use a job title of Senior Scrum Master. In fact I've seen many different job titles used for people in the Scrum Master role. The same goes for people in the Product Owner role.

From job titles alone, you can't really know the difference between a Scrum Master and a Senior Scrum Master. It's specific to every company. Often though, a Senior prefix to someone's job title means more working experience.

Take for example developers. You can have a Junior Developer, a Mid Level Developer, or a Senior Developer. When people talk about these different categories, they mean skills combined with time. The more time you work, the more things you end up knowing, the more skills you end up having, because you get exposed to more things in more time. It's just like in many aspects of life, like driving a car for example, or mastering the English language (even though you might use different titles, like Beginner, Intermediate, Advanced, Expert, etc). I've also encountered the term Junior Scrum Master. The train of thought is the same: time and skills. The salary also matched the title, of course.

When it involves extra responsibilities, beyond what a Scrum Master would normally do for a team or company, the job title usually changes. For example, a Scrum Master that trains other Scrum Masters and offers support for them is usually called an Agile Coach. If beyond offering training, the Scrum Master happens to manage actual work of multiple Scrum teams, and ensures collaboration and coordination between the teams (in other words, they are "hands on", not just a coach), the role is often named Chief Scrum Master.

The Scrum Master role and responsibilities are defined by the Scrum Guide. Any other job title prefixes/suffixes and responsibilities, are defined by companies for their own needs.

From a Scrum standpoint, there is no such thing as a senior scrum master. One could argue that it is a similar to a distinction like "senior" developer except that scrum has no space for hierarchy in scrum masters.

From a practical standpoint, I've seen it mean 3 things. First, it's sometimes a vanity title, just to add rungs on the ladder to climb. Other cases it might signify additional responsibilities (teaching, mentoring, etc). Many people feel that this is unnecessary since any experience scrum master should do this, but sometimes it helps to be explicit. The other distinction I've seen is in places with strongly-enforced salary bands. Adding adjectives like "senior" to a job title may be the only way to compensate an experienced person for their extra skill.

Exactly what it means really depends on the organization. However, there is one big red flag I look out for. It's one thing if the term senior scrum master suggests the person must have a high level of expertise in some or all of the scrum master responsibilities. However, it quickly becomes dysfunctional if the junior role is not expected to fulfill the duties of Scrum Master. For example, if a junior scrum master is only expected to schedule meetings and coordinate a task board, this is directly subverting scrum. All Scrum Master have coaching, facilitating, teaching, and championing responsibilities. You should have reasonable expectations of someone who is just learning, but those responsibilities are there still.