We are inviting a married couple to our wedding and both are doctors, the man is a medical doctor and the woman is a Ph.D. Do I address the envelope as The Doctors Smith, or do I keep their names separate, Dr. John Smith and Dr. Mary Smith?
The envelope can be addressed The Doctors Smith or if keeping the names separate, then the woman's name is first. If using their degrees, then leave off the "Dr."
Dr. Mary Smith and Dr. John Smith
Drs. Mary and John Smith.
Mary Smith, Ph.D. and John Smith, M.D.
There is some disagreement with the use of Dr. for a Ph.D. Traditional etiquette when addressing an envelope distinguished between a doctor of medicine (M.D.) versus a doctor of philosophy (Ph.D.).
Allexperts.com and Ehrenstein, et. al. (Everything Wedding Etiquette Book) feel that only a medical doctor should be addressed on the envelope as Dr. (http://en.allexperts.com/q/Social-Etiquette-Good-2570/Address-Dr-Mr.htm).
Mr. Hickey indicated that a Ph.D. uses Dr. when in a teaching or research position; otherwise Dr. is not typically used, unless you know their personal preference (http://www.formsofaddress.info/Doctorate.html).
However, it has become common to see someone with a Ph.D. addressed on the envelope as Dr., and as a consequence, deviation from convention has become acceptable.