Dear Miss Snark,
a few months ago, I sent a query to an agent and last week I received an email saying he wants to work with me. We exchanged several emails about his editorial suggestions (all good) and talked on the phone, but he didn't mention a contract. Is it customary to sign a contract with an agent as one does with a publisher? If so, how should I inquire about it?
Ask "do you offer a written contract".
Many agents don't. Good ones too.
The agency clause in a publishing contract will spell out some of the details when the work is sold.
I prefer working with a written contract but it's not a red flag if agents don't offer them.
You want to make sure you ask about stuff up front though: commission rates; corporate structure (LLC or sole proprietor); termination requirements etc.
A memo of understanding (like a deal memo) you send to an agent is also a good idea if they don't offer a contract.