Surface plasmon is the collective oscillation of free electrons in metallic nanoparticles. When two plasmonic nanoparticles are brought close together as a plasmonic dimer, their near field can interact with each other to generate new hybridized resonances. In particular, pairing nanoparticles with different optical, chemical, electrical, or mechanical properties as a heterodimer allows one to customize nanophotonic systems that utilize the desired features of individual components simultaneously. In this thesis, I present two examples to show the flexibility and modularity of such plasmonic heterodimers. In the first example, I demonstrate the use of Al-Pd nanodisk heterodimers as an antenna-reactor photocatalyst. A photocatalyst harvests energy from light to drive chemical reactions. Conventional catalysts are made of transition metal nanoparticles, which only interact weakly with light. On the contrary, plasmonic metals such as Al, Au, and Ag interact strongly with light, but are far poorer catalysts. By combining plasmonic and catalytic metal nanoparticles in one entity, the plasmonic antenna can drive a polarization in the catalytic reactor, creating a forced plasmon. This process dramatically enhances the optical response of the reactor, making it an efficient photocatalyst. Precisely defined, self-aligned, and strongly coupled Al-Pd nanodisk heterodimers can be prepared at the wafer scale using hole-mask colloidal lithography. Light-induced hydrogen dissociation reaction was performed as a model reaction to evaluate the performance of this photocatalyst. The wavelength- and polarization-dependent reaction rate closely follows the Al-mediated optical absorption of the Pd nanodisk. The high structural uniformity of the heterodimers also enables microscopic quantification of reaction rates and quantum efficiencies at single nanostructure level. In the second example, I investigate the optical properties of Al-Au nanodisk heterodimers. Both components of this heterodimer support surface plasmon resonances, but in different wavelength ranges. Forced plasmon can be created when the on-resonance nanodisk drives the off-resonance nanodisk through near field coupling. The hybridized resonances are not only observed with far field extinction spectroscopy, but also probed in the near field by photo-induced force microscopy. Moreover, when the interdisk spacing is very small and the near field interaction extremely strong, the Au nanodisk of the heterodimer can be repositioned and reshaped under laser illumination. This is attributed to a joint effect of photothermal softening of the Au lattice and the optical forces applied to the Au nanodisk. This thesis paves the way of designing and utilizing plasmonic heterodimers for a rich abundance of applications including photocatalysis, solar energy harvesting, sensing, and optically-induced nanomanufacturing.