It depends on the purpose of the résumé. If you're using it for job hunting,
you'll be told it shouldn't exceed one page ideally, two pages max. This can
be very difficult unless you've worked all that time for the same company.
If, on the other hand, you're a consultant (such as an expert witness)
providing a résumé to an attorney, the longer the better. One of my clients
has a résumé 16 pages long, including 11 pages of publications.