R.I. Gen. Laws § 15-3.1-2: Eligibility.

Persons shall be eligible to enter into a civil union only if both such persons are:

(1) At least eighteen (18) years of age;

(2) Of the same sex;

(3) Not a party to another civil union or a spouse in a marriage with any other person;

(4) Not in a family relationship within the degrees stated in Rhode Island general laws § 15-1-1 or § 15-1-2; and

(5) Neither person is mentally incompetent at the time of the civil union.