Ligand-stabilized nanoparticles possess size- and shape-dependent physical properties, and the ligand monolayers facilitate self-assembly. Several approaches for synthesizing, assembling, and transforming nanoparticles that result in novel optical and magnetic properties will be discussed: (1) A new method for tailoring the size and shape of Au nanorods gives control over their optical properties. (2) Electrospinning of aligned polymer nano/microfibers from Au nanorod/polymer solutions causes macroscale alignment of the nanorods, which imparts anisotropic optical properties. (3) Magnetic field-directed self-assembly of magnetic nanoparticles enables the synthesis of polymer composites containing embedded nanoparticle chains. (4) Nanostructural transformations accompanying the conversion of Ni nanoparticles into NiO and NixPy provide insight into the fabrication of heterostructured nanomaterials. (5) Deposition of thin Al2O3 layers onto monolayers of FePt nanoparticles promotes their sinter-free conversion from an alloy phase into intermetallics for magnetic recording.