The ISA, or International Society of Arborists, is a non-profit organisation which regulates arborist certification throughout the world. ISA certified arborists must meet stringent requirements, have extensive work experience, and pass a comprehensive exam before becoming a certified arborist. Certified arborists are trained in how to properly care for and remove trees as well as identify potential diseases, damage, and more. Only certified arborists can fill out arborist reports which are essential for distinctive tree permits needed to remove a tree.