Both First, it's important to realize there are many different kinds of librarians.
Librarians are highly educated people with varied interests.
Many librarians have more than one advanced degree in subjects ranging from anthropology to zoology and including business, law and Roman history. Because of this range, most libraries hire librarians by considering their institution's primary curriculum coverage. Library hiring committees look for people who will fill a specific need in a subject curriculum to aid in collection development, directly or indirectly, or with developing subject area information tools. In most institutions, there are librarians who organize resources, collect resources, evaluate resources and link resources. There are librarians who wheel and deal with vendors for the best prices for electronic as well as traditionally printed resources.