With this work, the author achieves the first comprehensive treatise on the effects of lex sportiva on contract law in international professional football as well as on the association law of FIFA members. He focuses on FIFA's regulations regarding the status and transfer of players and the jurisprudence of the Court of Arbitration for Sport (CAS), which acts as a professional instance in disputes within professional football. Special attention is given to the development of the substantive legal regulations that underlie the decisions of FIFA's association jurisdiction and the CAS. This is summarized under the overarching term lex sportiva.