Parental rights and signing requirements vary depending on your family dynamic and travel advisories. However, if both parents retain legal responsibilities to their child, it’s generally best to get their consent.
Parents who’ve separated may have an agreement that requires each parent to give permission for the child to travel. Or, if they’re divorced, they likely have a court order that addresses custody and decision-making authority when it comes to travel.
Keep in mind that if it isn’t possible to obtain consent—or if the other parent has no legal rights—you should carry a court order (or equivalent documentation, such as a parenting plan or consent order) to prove that you have sole parental responsibility.
If the other parent is deceased, you should carry the original (or a notarized true copy) of the death certificate.