Gadolinium (Gd) chelates have been extensively applied to enhance the imagery of anatomical tissues via magnetic resonance imaging (MRI). These molecular complexes have become some of the most common clinically applied contrast agents in modern medicine. The expansive development and clinical application of Gd chelates for MRI applications has led to a rebirth of interest in the use of Gd as a radiosensitizer in neutron capture therapy (NCT). However, the poor selective tissue labeling and localization provided by conventional molecular Gd chelates has limited success in both MRI and NCT applications. Methods for encapsulating Gd into nanoparticulate materials have been developed to overcome these limitations. Incorporating Gd chelates into nanoparticulate materials affords additional flexibility in engineering targeting and also provides a means to apply high tissue-centric concentrations of Gd - often critical for both imaging and therapeutic applications. The focus of this review is to summarize the evolution of engineered Gd nanoparticles, from self-assembled macromolecular structures to rigid particulate systems for enhanced MRI contrast and, separately, Gd NCT therapy.