In this project we investigate atomically thin, monolayer materials and their interaction with light. These materials are composed of a single sheet of a layered material, which is typically less than 1 nm thick. Despite of their low dimension, these monolayers may absorb more than 20% of the visible light, a first indication for their very strong interaction with light. In combination with their semiconducting properties, these material may be ideal building block of future optoelectronic devices. However, in this work we focus on a more fundamental effect, namely the strong coupling of excitons in these material with a confined light field. This effect results in the formation of new quasi-particles called excitons-polaritons. In many other materials this quasi-particles can only be observed at cryogenic temperature, but the very robust nature of excitons in these material allows to observe these fundamental effects even at room temperature. This is import to potentially exploit this effect for future applications.