The objective of the presented work is to facilitate the description of discrete-event models and the discrete-event part of hybrid-DAE models. It is achieved by combining the Parallel DEVS formalism, the process-oriented modeling approach and the Modelica language. This objective not only includes the description of P-DEVS and process-oriented models in Modelica, but also developing interface models which will facilitate the combination of these models with other continuous-time or discrete-event Modelica models. The development of this work includes the identification and analysis of the requirements needed to describe P-DEVS and process-oriented models in Modelica, the description and implementation of a message passing mechanism in Modelica, the implementation of the requirements analyzed into new Modelica libraries that facilitate the description of models using current Modelica functionalities, the combination of these new libraries with other Modelica libraries and the validation of the developed models using case studies and benchmarking systems.