The Big Ugly Question: Monograph or Serial?
Of course, you always want to check the catalog for an existing record before bringing in a new one, when cataloging in any format. However, this is especially important when working with conference proceedings because you need to make a determination about whether to catalog them as a monograph or a serial. Looking through catalog records can give you your first clues. If we've already cataloged it, stick with the existing format and just add an item record for the issue in hand.
Frequency Statement in the Title
The title may contain some wording that alludes to publication frequency, (e.g., The 14th Annual Conference of the North American Packagement Society). If you determine that the proceedings are published more frequently than triennial, the title should be cataloged as a serial. Anything cataloged less frequently than triennially will most likely be cataloged as a monograph, particularly something that looks like a one-off issue. Exceptions may be made to this policy if there is some compelling reason, such as a request from a collection manager to catalog the title one way or another.
If the proceeding has some subject-specific theme, (e.g., The 10th Annual Conference of the North American Packagement Society : Title Transfers, Friend or Foe?) we might be more likely to catalog it as a monograph. In this case, the monograph record would allow us delve more deeply into the subject of the title using more specific subject headings and the call number.