The thesis is a study of «manifestly ill-founded» and how it works as an admissibility criterion for the European Court of Human Rights. It is the admissibility criterion that is used the most out of the admissibility criteria for the European Court of Human Rights, and it has certainly played a very important role in enabling the European Court of Human Rights to weed out undeserving cases and cases that are not based on anything substantial. The development of the criterion is studied and is further used to highlight some of the criterion's drawbacks and benefits, and its role in the future of the Court. The use and interpretation of the criterion has received criticism throughout the years, the most central aspect of that criticism is that it has been interpreted too widely. This thesis addresses that and some other aspects of it that have been criticised.