The thesis Challenges of Implementing Prevention Programs in Schools covers the entire process of implementation of prevention programs, which is seen as a key component of achieving positive outcomes of those programs. The aim is to show the challenges, problems and barriers that are standing in the way while implementing a prevention program in a real-world school setting. Thanks to the increased attention to implementation over the last few decades, more and more is known about the factors that influence implementation and about the facilitators for a successful implementation. A small part of the study dedicated to implementation is focused on the detection of barriers and challenges to implementation. From the findings of available studies that are examining challenges of implementation in general or specifically in the school environment, a list of challenges facing the implementers (in the school environment that are mainly teachers) and programs while implementing prevention programs in a real-world school setting, is made. Challenges, barriers and problems are classified into four groups - (1) resources and assets, (2) prevention providers/teachers, (3) school climate and organization, (4) program and the wider environment. There are many obstacles that stand in the way of implementation and the most common barriers in the school environment are: lack of time, problems while scheduling the program, lack of resources and insufficient support to the program. Among available studies, only one offers potential solutions to these problems and obstacles. Since implementation moved closer to the focus of prevention science, there has been a lot of progress in that field. There are several reasons why study and monitor the implementation process, one of them being to detect problems and barriers which may impede the success of implementation and therefore the positive outcomes of the program. Authors agree that for the further development of implementation, a greater attention has to be drawn to investigating the problems and barriers to implementation. However, studies should not stop there. Solutions to the barriers and challenges facing implementation should be examined in the future.