Harilaos Koumaras (NCSR “DEMOKRITOS”) EVOLVED-5G’s Technical Manager presented the conference paper entitled “NEFSim: An Open Experimentation Framework Utilizing 3GPP’s Exposure Services” in the context of Session 8 of EUCNC 2022. Network Exposure Function (NEF) enables third-party application providers utilize the network capabilities and services that the 5G System offers. The 3rd Generation Partnership Project (3GPP) provides open standardized Application programming Interfaces (API) through NEF; however, a big gap appears in the market between mobile operators and service providers since no commercial solutions are available. In this context, the NEF’s standardized APIs offered by 3GPP are examined. As a result of this analysis an open-source simulator “NEFSim” is presented. NEFSim realizes the aspects of the NEF and enables application developers to experiment with the northbound APIs under a simulated, configurable environment. The paper has been created by Dimitrios Fragkos (National Centre for Scientific Research Demokritos (NCSRD) & University of Peloponnese, Greece), Georgios Makropoulos, Anastasios Gogos and Harilaos Koumaras (NCSR Demokritos, Greece), Alexandros Kaloxylos (University of Peloponnese, Greece & The 5GIA, Belgium).