‘Fundamentals’ outlines the scope of probability and outlines some basic approaches to determining it. Probability is the formalisation of the study of the notion of uncertainty. There are three main ways of thinking about probability. The objective approach simply counts the outcomes and assigns an equal chance to each, but counting the number of outcomes can prove troublesome. The frequentist approach uses experimental observations to estimate probability, but suffers from the same repeatability issues all experiments do. The subjective approach involves assessing chance based on experience and opinion. The subjective approach is most often used, but is at its strongest when augmented by objective and frequentist thinking.