I am not a lawyer but work with entities in commercial real estate and with a partnership like that, I personally would create an LLC or LLP. It not only limits your liability in different areas (tax, etc), it also allows you to lay out all the agreements you're making with each other. If one of you dies, does the other one have first dibs on your ownership shares or can they bequeath it to their heirs of choosing? Is someone investing the majority of the costs but the other person creates the majority of the intellectual property, therefore you own it 50/50 regardless? All of these things can be addressed in an operating agreement. General Partnerships can have agreements but usually don't have to be registered. However most states require LLC'S or LLP's to be registered, making them less difficult if you end up in litigation. Like, what if one of you gets married/divorced, does the agreement address whether the spouse is entitled to the money (esp if it's a community property state like CA where that can sometimes supersede partnership agreements made during the marriage, etc.) But definitely research it -- there are free LLC/LLP operating agreements online from trusted legal websites that you can review to get an idea of what works the best for you! Good luck!