The problem of illegal immigration has become one of the most intensely debated legal issues in Turkey. One of the consequences of this issue involves the expulsion of those who've entered the country illegally. Undoubtedly, expulsion decisions may be an issue not only for those who've enter the country illegally, but also for those who've entered the country legally. The phenomenon of illegal migration has two legal bases: human rights on one side and public order on the other, which cannot be neglected or ignored. An approach to dealing with this phenomenon that preserves both bases would undoubtedly be much fairer than a preference for one over the other. Secondly, the most important difficulties of proof in the judicial review of expulsion decisions, namely the difficulty of obtaining evidence to prove the acts alleged against the persons concerned and the evidentiary quality and strength of proof of the information on which the decision is based, will be evaluated in accordance with the decisions of administrative courts and the Constitutional Court. This study will first evaluate the nature of expulsion decisions in terms of administrative law. In this context, the study will answer the question of whether expulsion decisions are administrative measures or administrative sanctions. It will then indicate how the previous assumption of expulsion decisions being governmental acts is now rejected. Next, the study will analyze administrative proceedings with regard to the impact of the criminal investigations and prosecutions that constitute important evidence in the review of expulsion decisions. Lastly, the study will evaluate the standards of proof that may be applied in the judicial review of expulsion decisions and will state the standard of proof that this study believes courts should apply.