There seem to be a few schools of thought:

1) Pick a name that goes well with the first name
2) Pick a "backup" name, in the even that your LO doesn't like their first name
3) Use a family name from a relative or ancesor
4) Use the last name of one of the spouses (usually the person who changed their last name during marriage)
5) Use an ethnic name
6) Use a name with a deep meaning.
7) Don't have a middle name at all

For Olive, we went with #1 . Plus a variation of #4, except we used Bee's first name instead of her last name.

For Charlie, we went with #1 and #6. Bee had a dream about someone with the same name. Bee's name came to her dad in a dream too, so we took it as a sign.

Did you rely on any of the above techniques? Curious how you picked your LO's middle name!