Disclaimer: I'm not a lawyer, and am not providing legal advice. I am, however, closely related to a partner at a CPA firm who deals with this sort of fall-out

Disclaimer: I'm not a lawyer, and am not providing legal advice. I am, however, closely related to a partner at a CPA firm who deals with this sort of fall-out all the time. The lack of documentation is hugely problematic, and will only be settled by negotiation or court. In this case your equity stake in the company is going to be parsed by the court according to your initial contribution to the company (not total contribution, INITIAL contribution)... particularly money. They're going to try and figure out who put money in and when. They'll use that to arrive at an equity figure and current valuation. This is a really expensive forensic process, so.. uhm.. be prepared. There are some pretty interesting tax implications here as well. In some cases the court will grant additional equity to a founder based on some metric for amount of work, or expectation of the role at founding. This can have some interesting tax implications, as the IRS will view that additional equity as income (and thus the starting capital for the company becomes a huge deal). That's just the tip of the iceberg here, sadly. I've seen this go in a variety of directions based on verbal agreements, agreements with folks outside of the company, and the general mood of the litigators working through this. One thing you SHOULD talk to a lawyer about is how long you have to make the claim. Often folks will just sit on the sidelines and wait to see if the company goes anywhere. Once it does, they THEN move after their 'rightful' equity as there is some actual cash to be had. Spending thousands (if not hundreds of thousands) of dollards on a lawsuit for a company that will likely never make a dime doesn't seem very smart.