Collecting for Library Use – A Wonder

In terms of topic oriented collecting, where does one topic stop and another begin? Can we define this line? Is a library, public of academic, supposed to collect all publications by a popular fiction author? Or must we think of this as excessive? If we collect all of an author’s published works, do we also decide to collect monographs on said author? And what about books that might be defined as relevant to understanding context to that author’s works or writing space? And we have not even considered all formats relevant to each topic. Questions abound in library collection development

I have no answers here. The above link to Wikipedia is for dialogue purposes only. I just mean to invite conversation. Please weigh in. I welcome comments here  (moderated) or @ Twitter.

Thank you much.
There will be more in the future.