Bismuth nanoparticles (Bi NPs) for use as an X-ray contrast material have gained significant traction in recent years due to the high atomic number and generally accepted biological tolerance of bismuth. However, to be considered a viable candidate for use in this application, water solubility is a necessity, which poses a challenge, since bismuth tends to readily oxidize. For this reason, research into the direct aqueous synthesis of Bi NPs is still in its infancy and can be very difficult, as described in Chapter 1. The remaining chapters of the thesis describe the direct aqueous synthesis of Bi NPs starting from a water-soluble bismuth tartrate (Bix(D-TA)y) precursor. Syntheses were carried out in an aerobic environment using a variety of pH and temperature conditions, from biologically compatible and inexpensive chemical reagents. Chapter 2 describes initial studies that sought to use glucose as the reducing agent and its oxidation product, gluconic acid, as the surface-stabilizing species. These studies showed glucose to be ineffective as a reducing agent for bismuth, as reactions progressed slowly and resulting particles lacked size and shape uniformity. The addition of a co-reductant, borane morpholine, was observed to result in an increased reaction rate, which yielded particles that exhibited improved size and shape uniformity. However, due to lack of surface stabilization, resulting particles were often observed to undergo oxidative dissolution upon quenching of the reaction. To better stabilize particle surfaces, glucose was replaced with 300 MW poly(ethylene glycol) (PEG 300). This change resulted in an overall decrease in the rate of reaction. The majority of syntheses using PEG as a surfactant resulted in Bi NPs that were equally unstable, as particle colloids were often observed to dissolve when quenching the reaction. For samples in which oxidative dissolution did not occur, the resulting Bi NPs were observed to be crystalline, aggregated nanostructures lacking any size or shape uniformity. For samples that underwent immediate oxidative dissolution and were afterwards left in a closed container absent of light for ~96 hours at room temperature, regrowth of Bi NPs was observed, where particle growth was thought to occur through a seed-mediated pathway. Through this seed-mediated growth method, resulting Bi NPs were observed to have significantly improved size and shape uniformity, as well as aqueous colloidal stability. Chapter 3 describes additional syntheses that yielded highly stable and relatively size uniform aqueous Bi NPs, which were prepared by chemical reduction of the same Bix(D-TA)y precursor. In these studies, hexamethylenediamine (HMD) was used as the surface-stabilizing agent in place of PEG 300. Analysis via FTIR revealed the presence of the ligand tartrate, which facilitated a simple acid/base titration method of particle isolation. With the addition of HCl, particle colloids would flocculate, allowing for ease of separation from the reaction medium by centrifugation. The Bi NPs could then be re-dispersed in aqueous solution with the addition of NaOH.