Hi Cyath,

Are you saying that you have a finished non-fiction manuscript? Either way, non-fiction and fiction submissions generally work on a 'taster' basis. If the agent/publisher likes the sample/proposal, then they'll ask to see more. Some will be happy to review the whole thing, but since they are inundated with submissions, they tend to want people to stick to the process they set out on their website.

However, if you have a completed manuscript, this is definitely something worth mentioning in your proposal. Fiction proposals require you to have a complete ms (and they can get shirty if they read your sample and ask to see the rest of it, then you tell them it's not finished!). However, non-fiction is generally more relaxed, and while it's better to have the whole thing complete before you submit, it's primarily the idea that's being assessed, so partial completion is not unusual.

Lastly, proposals also do more than lay out the idea; they tell the agent/publisher about you, your credentials, where you see the book selling, why there's a demand for it, what competing works there are, and so forth. Sadly, it's all about the money, these days, and the more you can do to convince them that you're a potential money earner, the better.

Good luck!