The current role of rare-earth-element- (REE-) and actinide-bearing accessory minerals as both geochronological markers and recorders of geochemical processes is reviewed in this paper. The minerals covered include the most common REE- and actinide-bearing accessory minerals found in high-grade rocks—i.e., monazite, xeno-time, apatite, huttonite, thorite, zircon, allanite, and titanite. The goal of this review is to describe the most recent research developments regarding these minerals and their interaction with each other as well as their role as geochronometers. These results are then applied to two cross sections of lower crust from Rogaland–Vest Agder, SW Norway, and Tamil Nadu, S India...