Ultra-reliable low-latency communications (URLLC) has been considered as one of the three new application scenarios in the 5th Generation (5G) New Radio (NR), where the physical layer design aspects have been specified. With the 5G NR, we can guarantee the reliability and latency in radio access networks. However, for communication scenarios where the transmission involves both radio access and wide area core networks, the delay in radio access networks only contributes to part of the end-to-end (E2E) delay. In this paper, we outline the delay components and packet loss probabilities in typical communication scenarios of URLLC, and formulate the constraints on E2E delay and overall packet loss probability. Then, we summarize possible solutions in the physical layer, the link layer, the network layer, and the cross-layer design, respectively. Finally, we discuss the open issues in prediction and communication co-design for URLLC in wide area large scale networks. * Accepted by IEEE Vehicular Technology Magazine, 2019. example, in LTE systems, the control signaling for uplink (UL) scheduling leads to a high latency that is much longer than 1 ms in the control plane [3]. Thus, how to design grant-free access techniques for URLLC deserves further study. Besides, with the first-come-first-serve (FCFS) scheduling policy, the short packets of URLLC services may need to wait for the processing of long packets of eMBB services. Thus, FCFS policy may not be the optimal policy for short packets in URLLC services, and other policies should be considered to minimize the E2E delay.The current techniques in the 5G NR [4] mainly focus on achieving the target E2E performance in local area communications, where all the user equipment (UE) lies in one or few adjacent cells. For different communication scenarios, the network architectures are different. In factory automation, the communication area is limited in a smart factory, while for remote control, the controller and slave can be located on different continents. As a result, the latency in radio access network only contributes a small portion of the E2E delay, and other delay components such as core network delay over a long distance large scale network and processing delay in the computing systems may be the dominant components [5]. Therefore, how to improve the E2E performance with different network architectures is still a challenging issue.In this paper, we focus on how to guarantee the E2E delay and overall packet loss probability in different communication scenarios, including local area communications, mobile edge computing (MEC) systems, and the long distance large scale networks. The rest of this paper is organized as follows:• We elaborate possible components of the E2E delay and overall packet loss probability in typical communication scenarios, and provide a general way to formulate the quality-of-service (QoS) constraints of URLLC.• We summarize possible solutions and techniques in physical layer, link layer, network layer, and cross-layer design aspects for URLLC...