In recent years, we have seen an increasing interest in immersive mobile multimedia applications and services. Advanced human-machine interfaces (HMIs) and related head-mounted displays (HMDs) support different levels of computer-generated virtual worlds. These worlds include mobile virtual reality (VR), mobile augmented reality (VR), and mobile mixed reality (MR) which are jointly captured under the term mobile extended reality (XR). In addition, the development of fifth generation (5G) mobile networks aims at catering for ultra-reliable low-latency communications such as mobile XR and the tactile Internet. In this context, 5G mobile networks are essential enablers to carry mobile XR beyond video gaming to the general consumer and industry markets. In this keynote lecture, the fundamentals of interconnected immersive mobile multimedia are reviewed, and opportunities, challenges, and enablers are discussed. An overview of immersive mobile multimedia from mobile video to mobile 360-degree video, mobile VR, mobile AR, mobile MR, and mobile XR is provided. Major components of interconnected immersive mobile multimedia will be discussed and application opportunities in different vertical industries are pointed out. Furthermore, challenges associated with the delivery of immersive mobile XR applications are shown through service integrity parameters. Several enablers for interconnected immersive mobile multimedia applications are highlighted including standardization activities.