An Arborist by definition is an individual who is trained in the art and science of tree planting, caring for and maintaining individual trees. Certification is a non-governmental, voluntary process by which individuals can document their base of knowledge. It operates without mandate of law and is an internal, self regulating device administered by the International Society of Arboriculture. Certification is a measurable assessment of an individual's knowledge and competence required to provide proper tree care. 
Certification is not a measure of standards of practice. Certification can attest to the tree knowledge of an individual, but cannot guarantee or assure quality performance. Certified Arborists are individuals who have achieved a level of knowledge in the art and science of tree care through at least three years of experience and have passed a very comprehensive examination developed by some of the Nation's leading tree care experts.