As progress was made in the sphere of mathematics one has tried to discover methods for calculating pi. Therefore, studying the history of pi makes you go through geometry, analysis, special functions, numerical methods, algebra and number theory. I have for every epoch taken into account important results, from the time when one wished to construct a quadrate with the same area as a circle and get pi to be exact, until one was able to prove the opposite, the irrationality and transcendence of pi. The periodicity of circles and functions is dealt with to explain why pi occurs in many other areas within mathematics and other sciences.