The development of well-controlled synthesis of metal and metal oxide nanocrystals (NCs) via the colloidal method enables a high degree of control over size, morphology, and composition. The well-defined NCs could potentially overcome the traditional structural heterogeneity observed in conventional synthetic methods and open up new opportunities in systematic studies of their catalytic activity and magnetic properties. In this work, we focus on exploiting the composition- and crystal structure-dependent properties of monodisperse bimetallic NCs to establish the structure-property relationships of thermal, electro-, and photocatalytic performance. Specifically, we show that the selectivities for the hydrodeoxygenation reaction of biomass-derived molecules are strongly dependent on the bimetallic NC compositions and supports. By designing an operando X-ray cell, we identify the active structure under reaction conditions that are responsible for the catalytic performance, and thus aids research efforts towards developing the best possible catalytic materials for biomass-upgrading applications. Next, we demonstrate how the control of crystal structure can contribute to superior electrocatalytic oxygen reduction reaction activities. The intrinsic correlation is established between the relevant catalytic activity enhancement, the chemical compositions of bimetallic NC catalysts, and the ordering structures at the atomic scale. Finally, we combine the versatility and precision of NC synthesis with surface ligand chemistry to establish a fundamental understanding of magnetic properties. The design of dendritic ligands on the surface of magnetic metal oxide NCs provides insights into the NC size and inter-particle spacing dependence of the static and dynamic magnetic properties useful for designing high-frequency, low loss materials.