This document aims to describe grain boundary responses in body-centered cubic (bcc) materials to absorption of dislocation loops, to improve understanding of component phenomena of radiation damage in materials.First, it introduces the context of radiation damage in materials and the broader importance of understanding related material behavior and provides background on grain boundary structure and defects, introducing approaches that will be used in the following chapters. A $\Sigma$5 $(210)[001]$ STGB in Fe responding to absorption of different sizes of interstitial and vacancy loops exhibits both a DSC-disconnection reaction and some extent of a state change response concurrently, though with extent of each depending on the size and character of the inbound loop. The detailed state changes observed in a $\Sigma$5 $(012)[100]$ STGB in Mo after absorption of interstitial loops and the disconnection reaction response to interstitial loop absorption in $\Sigma$13 $(0\bar{3}2)[100]$ and $(0\bar{5}1)[100]$ STGBs in Mo are also described. The document then presents an approach to characterize defect absorption by GBs in experimental settings by linking atomistic descriptions of absorption phenomena with experimental Nye tensor measurement changes. The overarching conclusions from all of the work discussed are that the interaction of dislocation loops and GBs, and the loop absorption response of the GBs depend on the loop and GB involved. Specifically, the available possible dissociations of the Burgers vector of the loop in the GB and the available GB metastable states with the same macroscopic orientation are important considerations. The hope is that understanding these cases of single-loop absorption and resulting GB responses will then be expanded to more complex systems, longer timescales, and larger-scale loop and mixed defect absorption to provide more detailed understanding of GB evolution (and factors affecting it) throughout the process.