Since my students are learning to use dichotomous keys in science, I created one for them to use with numbers. They are still not quite sure about how to classify numbers so I thought that they could practice dichotomous keys and real number classification at the same time. The key also includes reminders, such as "All whole numbers are also integers". The key results in classification as counting (natural) numbers, whole numbers, integers, rational numbers, irrational numbers, and imaginary numbers. The key allows them to easily sort numbers into a set.