According to the 7th Judicial Circuit Court of Clay County, Mo., custody is a legal arrangement made by the court for the parents of a minor child. Guardianship is a court-ordered arrangement for the care of a minor child by a qualified third party. Guardianship is assigned to a qualified adult when a minor's parents are unwilling or unable to fulfill their obligations as parents.
The court further explains that in Missouri, custody is determined in family court while guardianship is awarded by a probate court. Guardians are often close family friends or adult relatives of the minor. A guardianship is awarded by the court when the child's parents are deceased or deemed unfit by the court. Guardians are required by law to act in the best interests of the child and make decisions regarding education, support and care until the child turns 18 years old and guardianship is terminated.
The court also notes that the minor's parents are legally considered to be the child's guardians and thus do not have to be appointed by a court. Custody is determined by the court when the parents divorce or otherwise do not live and work together as a parental unit. Typically the parents are given joint custody by the court, an arrangement where both parents are both allowed to provide for and spend time with the minor. In Missouri, custodial arrangements are determined based on what is in the best interests of the child.
These two terms are similar but legally different and often interact in complex ways. Courts resolve any conflicts by asking what is in the best interest of the child.