The moment I learned that my arboriculture professor was an ISA Certified Arborist, I knew that was what I wanted to be as well.  I wanted to know everything about trees. Studying for the ISA certification exam provided me with a much greater knowledge of trees and how to care for them. Now with years of experience and continuing education to maintain my certification, I have come to realize that when you know enough to pass the certification exam, that is really the minimum of what someone needs to know to effectively work with trees. For that reason, when hiring a contractor in instances when a tree is involved, I strongly advise contacting only ISA Certified Arborists. From that list, pick the one you feel is the most qualified. I encourage you to learn more about the ISA certifications and visit the ISA website.