IANAL, but here is what I would do at a minimum. First and foremost make sure you have a shareholder agreement that clearly lays out what your role is and what

IANAL, but here is what I would do at a minimum. First and foremost make sure you have a shareholder agreement that clearly lays out what your role is and what is expected of you. It really doesn't sound like you are taking any risk (i.e. you are keeping your job, you are going to continue to work on your own projects), so the bigger question is how much time and value are you really adding to the startup? You will want to be clear in your agreement what your intentions are and how much time you are willing to devote. While telling your co-founder that you plan to keep your job and work on other projects sounds good in theory, when something doesn't get done or a milestone is missed, you are going to be the easy target for that failure. Startups are risk inherent, and if you don't have any tolerance for risk they definitely are not for you. Animosity can fester when one founder is taking all the risk and the others are just along for the ride. From your side things you may want to clarify are what your ownership percentage is, what the vesting is going to be, are you getting paid and if so how much, what your duties are, etc.. After you have a shareholder agreement drawn up, it is better to spend a couple hundred dollars to have your own attorney review it. Those dollars spent now could save you aggravation or even costly expenses down the road.