Cellular communication networks are commonly utilized for connecting DERs. Nevertheless, conventional cellular networks prior to 5G were unreliable while private cellular networks incur huge investment costs. Radio access network (RAN) slicing in 5G communications can address these issues by providing the VPP with virtual private networks in public cellular networks. The VPP must evaluate the benefits of 5G RAN slicing and determine the size of slices before implementing it. This chapter proposes to apply 5G RAN slicing to assist the VPP to participate in frequency regulation services. First, an optimization model is developed for the VPP to maximize the profit of engaging DERs in various frequency regulation services. Its solution determines the VPP’s scheduled DER portfolio of regulation services and communication needs. Then, the effects of public shared communications on the regulation performance are quantified. 5G RAN slicing enhances the predictability of communication reliability, and its benefit is explicitly modelled as its contribution to reducing the risk of the VPP’s profit loss. Next, based on the 5G RAN slicing benefit, an optimization model for determining the size of slices is further established, considering the cost of purchasing slices from mobile service providers. Additionally, an online solution method is developed, such that DERs’ regulation service portfolio can be determined in real-time. Numerical case studies are conducted to demonstrate the benefit of 5G RAN slicing for the VPP’s frequency regulation services.