This chapter focuses on the basis of decision-making: immigration law, examining how it is constituted and worked with the two factors, constitution and implementation of law, are intrinsically intertwined. Since immigration law directly impacts and depends upon other fields of law, many officials are expected to have knowledge of the basic welfare laws, criminal law and, of course, executive laws for the administration. The analysis of immigration law, exemplified by the examination of the impact of the Ankara Agreement and the decisions of the European Court of Justice, questions conceptions of law as black letter text which can form a basis of analysis or decision-making. Finally, the findings of concur with classic studies on bureaucracy that street-level officials do wield considerable amounts of individual autonomy and can thus use and abuse their discretion both during the decision-making process and in the decisions themselves.