When you list 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 Justice, 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. It's often easier to simply rearrange a sentence.
Not: Justice, Health and Social Services and Community Services all worked on the project.
But: Justice, Health and Social Services, and Community Services all worked on the project.
We base our style for commas on The Canadian Press Stylebook.