When listing items in a series, do not put a comma before the “and.”
Not: There were seniors, Elders, and committee members at the meeting.
But: There were seniors, Elders and committee members at the meeting.
Sometimes, however, we write lists where one of the items in the list has an “and” in it, such as “Health and Social Services” in this list:
The departments of Economic Development, Health and Social Services and Community Services
In such cases, it might be clearer for the reader if you add a comma before the final “and.” (This is called a serial comma or an Oxford comma. We do not follow this style as a rule, only when it’s necessary for clarity.)
Not: Economic Development, Health and Social Services and Community Services all took part in the project.
But: Economic Development, Health and Social Services, and Community Services all took part in the project.