###### Abstract
To address the issue of mitigating multicell D2D underlay interference, _[PERSON], [PERSON]_ and _[PERSON]_[5] proposed a two-step approach, which involves solving the initial resource block allocation problem by formulating it as a bilateral symmetric interaction game, and then addressing the transmit power allocation problem by using a linear programming approach to minimize the total interference of the network. In order to respond to changing network conditions, there is a need for the resource allocation mechanism to be adaptive. The paper by _[PERSON], [PERSON], [PERSON]_ and _[PERSON]_[6] presented a cooperative reinforcement learning algorithm for adaptive allocation of resource blocks and transmit power to D2D users in a cellular network. By efficient control of the interference level, the proposed algorithm results in improved overall system throughput, D2D throughput and fairness among D2D users. The spectrum efficiency problem in group D2D communications is next addressed by _[PERSON]_, _[PERSON]_, and _[PERSON]_[7] who proposed a QoS based non-orthogonal multiple access (Q-NOMA) scheme in which D2D users in a NOMA transmission are ordered according to their QoS requirements. Using stochastic geometry tools, the authors modeled the spatial relationships and interferences between the group D2D users, which led to a closed-form expression for characterizing their outage performance. In human-centric D2D communications, the social and trust relationships between users are humanistic features that can be leveraged for enabling more secure and reliable solutions. _[PERSON], [PERSON], [PERSON]_ and _[PERSON]_[8] exploited the social relationships among D2D users to model the trust level between them, and proposed a social trust-based solution for enhancing the performance of D2D-enhanced cooperative content uploading in the presence of packet dropping or corrupting malicious nodes for narrowband-IoT cellular environments. In another cooperative design, _[PERSON], [PERSON]_ and _[PERSON]_[9] considered the problem of relay-assisted cooperative multicast (one-to-many) D2D communications, and presented a relay selection scheme that considers both propagation link conditions and relay's social trust level with the constraint of minimizing end-to-end delay in an integrated social-physical network. Besides multicast, broadcast (one-to-all) is another communication option that can be supported by D2D. This special issue concludes with a paper by _[PERSON], [PERSON]_ and _[PERSON]_[10], who proposed a message broadcast solution appropriate for vehicular networks based on multihop D2D communications. The proposed solution allows a user to specify its target area without being constrained by cell boundaries. It relies on application-level device intelligence and standard D2D resource allocation methods of LTE-A to enable fast, reliable and resource-efficient message broadcast services. The Guest Editors wish to thank all the contributing authors, the professional reviewers for their precious help with the review assignments, and the excellent editorial support from the Future Internet journal at every stage of the publication process of this special issue. All three authors contributed to making the editorial decisions on the submissions to this special issue. B.-C.S. prepared this editorial with some inputs from S.F.H. and P.H.-J.C. The authors declare no conflict of interest.