Judith E. Brandt has written a book called The 50-Mile Rule: Your Guide to Infidelity and Extramarital Etiquette. Here is an excerpt of an interview Brandt did with the Chicago Tribune:

Q: You work for a humor magazine. Is your book some sort of wicked satire?

A: No. This is not a National Lampoon take on adultery. This is serious information presented in a fun way. There are no books out there on this subject in a format that is not judgmental. I want to help people make smart decisions before they make that step.

Q: What about the ethics and morality of extramarital affairs?

A: There is a simple answer. Affairs are immoral and wrong. But the reality is that people are having them anyway. So you have to meet people where they are. For a lot of people, morality doesn't end up in it. So if people are doing it anyway, you have to try to mitigate the hard edges.

Q: You say [in your book], don't feel guilty. That doesn't seem realistic.

A: Guilt is basically something built into society to keep you in line. If you are going about your business in a discreet way and you are continuing to take care of your wife and, most importantly, your children, there is no reason to feel guilt.

Q: Say a friend said they were considering getting involved in an extramarital affair and asked for your advice. What would you tell them?

A: The advice I would give is that it is based on your needs. People enter into [affairs] for many reasons. It's not always just sex. There are emotional needs. As far as I'm concerned, affairs can serve some short-term tactical needs in a long-term relationship strategy.