It’s fair to follow up with them if you haven’t heard back after six weeks; it’s likely an oversight. Send an e-mail that says you are checking in to see if they had a chance to consider your query and that you look forward to hearing from them soon. Be emotionally detached, and don’t take it personally. If you don’t hear from them, move on to other agents. Your letter may be in a pile on an overwhelmed assistant’s desk, or stuck in his e-mail inbox or in his desk drawer. Or it’s in a stack the agent intends to get to, and feels guilty about not addressing more quickly. Unfortunately, most agents do a kind of triage on the volume of material that moves through their office—but most of them take queries seriously.
About three months ago, I sent a synopsis of my novel as well as a cover letter to six literary agents whom I researched and found to be interested in the kind of fiction I write. I haven’t heard from any of them and I’m wondering when I should follow up with queries about my proposal. I don’t want to be pushy, but at the same time, life’s short.