The outstanding importance of phosphorus (P) in all living cells makes it an essential nutrient. Its pivotal use as a fertilizer and the finiteness as a natural resource lead to a new episode of historic importance: A possible upcoming phosphate crisis. In this book an overview on the role of phosphorus as a nutrient and as a fertilizer as well as the underlying soil dynamics is given. The flows of phosphorus in Austria are shown by using the method of material flow analysis (MFA). Furthermore, a ‘System Dynamics P-Model’ was developed to outline the characteristics of phosphorus and its use in soils. This model considers the complex interactions and processes in soils. It shows the influence of soil properties, the effects of fertilizer use and crop uptake, and their dynamic interrelations.