I am not a lawyer, and you should talk to one. But, before that - there are a couple of thoughts that might help: You should have a broad agreement before you

I am not a lawyer, and you should talk to one. But, before that - there are a couple of thoughts that might help: You should have a broad agreement before you go to the lawyer. Are you thinking about a 50% share in the company or a 1% share in the company. You need to talk about it and be on the same page. After you talk about it, I would just get a confirmation via e-mail. Some documentation is better than no documentation. (Yes, you ideally want a lawyer looking at it, but it also would be a legal liability for him if there is a rough e-mail agreement that he hasn't given you shares for). The idea guy will likely want you to be working full time on the company. I think your answer should be something of the order of 'Yes, as soon as you are also full time meeting goals XYZ and that we have enough runway to pay me 50% salary for 18 months'. Until the company exists any work that you have done you own it (unless he has paid you and you have explicitly assigned the IP to him). If he waits for investors before incorporating, there is going to be a tax situation (because then the company will be worth something). You ideally want to incorporate and value the entire company in the beginning at $1 or something similar. Most investors will likely want the technical talent that they are investing in. If he gets good investors then they will likely want you to have an comparable share in the company as him. However, in my opinion, your worst case scenario is that he could say to the investors you are not too important, and that he can toss your code and get it built offshore for cheap (which might be easy given that there is an already working prototype).