This is fairly straightforward. In joint custody both parents would communicate on all decisions made for the child (where they live, their healthcare, their education etc.) with the best interest of the child in mind. With sole custody one parent has the sole responsibility (and right) to make all decisions about that child without consulting the other parent. Joint custody is the presumption in New Mexico. What this means is that unless there is evidence that sole custody is in the best interests of the child, the court will award joint custody.