Sole custody exists when one parent has the exclusive right and obligation to make decisions about the child's upbringing. This includes making all decisions about the health, education, and welfare of the children. Joint custody, also referred to as joint legal custody, means that both parents have equal decision making power with regards to medical, educational, religious, and other major decisions for the child. One parent cannot exclude the other from the decision making process, except that joint custody orders may give one parent final say over some areas of decision making (e.g. educational) and the other parent over other areas of decision making (e.g. non-emergency medical decisions). ("Joint custody" may sometimes be improperly used to refer to situations where the children spend almost equal time at each parent's house; however, equal-time arrangements are more correctly described as "shared [physical] custody, and do not automatically signal whether the parents have joint legal custody for decision making.)
It is common for parents to have joint legal custody; but one parent will have primary physical custody, and the children will spend most of the time living with that parent, and spend alternate weekends and certain days of the week visiting with the other parent. In this case, both parents must still be involved in all decision making for the child.
In New York, there is no statutory joint legal custody, so after trial, a judge can only award sole legal custody to one of the parents, granting all major decision making to that parent. However, if the parents agree to joint legal custody, a judge could make it a legal order of the Court and enforce it. If a parent violates the joint legal custody order in any respect, the other parent may make an application to the Court to enforce the order or to modify the order to sole legal custody to the primary physical custodian, on the basis that the parties cannot cooperate to implement joint legal custody.
In my experience, for fathers who do not expect to be awarded primary physical custody, more equally shared time with the child is far more valuable than being awarded "joint legal custody" but only weekend visitation with the child. It is the sheer amount of time and daily interaction that makes the richer relationship possible. And even without joint legal custody, a non custodial parent still makes day-to-day decisions for the child on the days the child is with him.