For what period of time are employers required to keep a) solicited and b) unsolicited resumes on file? We have very limited file space and would certainly prefer not to keep them past 3 months if possible! Thank you.

You do not need to keep unsolicted resumes longer than the time it takes you to read it (I figure 1.25 seconds).

However, if you decide to keep ONE such resume, you better keep them ALL and retain them just like you do solicited resumes and applications -- one year for most employers, two years for federal contractors.