This reprint mainly focuses on the latest challenges in PNT, especially in challenging environments for various research investigations and a range of practical applications. Topics cover high-precision and high-reliability PNT with GNSS or multi-source sensors, resilient PNT with GNSS or multi-source sensors in challenging environments, integrated PNT with GNSS and multi-sensor systems, and applications of PNT with GNSS or multi-source sensors.