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MODS has various elements for dates: dateIssued, dateCreated, copyrightDate, and others. After discussions both on and off of the zotero-dev google group, I wanted to seek clarification of what was intended to be put in each of these elements (particularly the copyrightDate field). MARC 260$c was for the "date of publication, distribution, etc." It would often be used to store the date from the copyright page of a book. The field could also include a copyright date, often prefixed by a "c". I suppose that the copyright page of a book may differentiate two separate dates or the copyright registration records could be consulted for that. A lot of MODS records that have been converted from MARC therefore put 260$c into dateIssued unless the date is prefixed by a "c", in which case they use "copyrightDate". But it is not clear to me that modern data should embrace these legacy conventions. One example is Bruce D'Arcus's book "Boundaries of dissent : protest & state power in the media age." cocatalog.loc.gov gives the following dates: Registration Date: 2005-12-02 Date of Creation: 2005 Date of Publication: 2005-11-18 amazon.com gives what is presumably a date of distribution: 2005-11-24 although other sellers give the date as: 2005-11-22 the copyright page at the front of the book claims: 2006 The last of these is what is traditionally cited in a bibliography, I think. Traditionally, it has certainly been the easiest date for readers to find. The popularity of online book sellers has made the the distribution date quite easy for readers to find as well. I would therefore expect reference management software to give preference to these two bits of information over the more mundane details of copyright registration. An export may look like: <originInfo> <dateIssued encoding="w3cdtf">2005-11</dateIssued> <copyrightDate encoding="w3cdtf" keyDate="yes">2006</copyrightDate> </originInfo> dateIssued is "the date that the resource was published, released or issued." Comparing cocatalog & amazon, we see that these dates can actually differ. In this example, they're close enough. copyrightDate is "a date in which a resource is copyrighted." In Berne convention countries, the copyright date is the date of creation. The copyright registration may be a different date (it is encouraged to be done within five years of publication in the US to be prima facie evidence), but the MODS documentation does note specify that this is intended to be a registration date & this seems more tedious for catalogers and citation managers to find. I have chosen the date provided in the copyright notice because of my bias for using this in reference management software. I don't know if this bias is that different from other catalogers, who will key info from the physical monograph, though. As Bruce said "MODS is maybe a little too clever on dates for its own good." However, I thought I'd make sure that we're not missing anything & are encoding this as well as possible, given the constraints. --Richard Karnesky