Countries with proportional representation are increasingly introducing an electoral threshold to stop smaller parties from entering their parliaments. In this paper, I’m focusing on the  proportional electoral system and mainly why some countries choose to impose a barrier to their parliaments and others do not. First I did a survey to see which countries that are using it and after that I decided to do three case studies including: Sweden, The Netherlands and Turkey. I used Carles Boix theory on proportional electoral systems. The main variable in his theory is that the “threat” from the social democratic parties has an affect on the enforcement of a PRsystem. I wanted to examine whether it was possible to apply this theory on the implementation of thresholds. Finally, it is possible to conclude that Boix theory can be used even when studying the emergence of electoral barriers. Boix theory suggests that any "threat" from new parties makes the old, larger and established parties or other government organizations want to impose a threshold to secure their positions. This was the case in Sweden and in Turkey. In countries where this situation does not exist, it seems to be no need for an electoral barrier, as shown in the Netherlands.