We review the physical mechanisms that allow tuning of absorption and emission characteristics in monolayer semiconductors. We use the model system of transition metal dichalcogenide mono-layers such as MoSe$_2$ or WSe$_2$ due to their very efficient light-matter interaction and availability of high quality samples. For monolayers encapsulated in hexagonal boron nitride both homogeneous and inhomogenous contributions to the exciton optical transition linewidth can be tuned opening up pathways for tailoring the reflectivity and absorption in van der Waals heterostructures.