You are not legally required to sign: the lender could choose to give the loan without your signature. On the other hand, the lender does not have to loan your husband--it is purely voluntary for him to do so--and since it is voluntary, can put any requirements on it that he likes: e.g. the lender could refuse to make the loan without you cosigning.As to whether you *should*--we can't answer that for you. You have to balance that fact that if you don't sign, you are not personally liable (his share of or interest in marital or joint assets are at stake, but not your personal, separately owned assets or income) and therefore, if you do sign, you are making yourself liable, vs. your family's need for this loan. If you want to stay separate from your husband's venture or don't want to put your own assets at risk for this reason, then you probably should not sign.