Understanding and tailoring light-matter interactions is critical to many fields, offering valuable insights into the nature of materials, as well as allowing a variety of applications such as detectors, sensors, switches, modulators, and lasers. While reducing the optical mode volume is critical to enhancing the light-matter interaction strength, plasmonic systems, with their extraordinary ability to confine the light far below the diffraction limit of light, provide intriguing platforms in boosting the light-matter interactions at nanoscale. On the other hand, atomically thin semiconductors such as few-layered transition metal dichalcogenides (TMDs), a recently discovered class of materials, exhibit unique optical properties such as large exciton binding energies, tightly-bond trion excitations, and valley-spin locking, allowing the observations of interesting photonic and electronic phenomena including strong photon-exciton coupling, valley Zeeman and valley optical Stark effect, valley Hall effect, and spin light emitting, hence serve as great candidates to study light-matter interactions in two dimensional systems. In this thesis, combining the two intriguing optical and material systems, we study light-matter interactions between 2D semiconductors and 2D plasmonic lattices, due to their compatibility with 2D semiconductors as well as strong and highly tunable plasmonic resonances. We investigated exciton-plasmon coupling by integrating MoS2 with plasmonic lattices of various geometrical designs and observed rich phenomena in different coupling regimes. We will first present a detailed study of observing exciton-plasmon coupling in weak, intermediate and strong coupling regimes via different plasmonic lattice design. We’ve demonstrated large Purcell enhancement in weak coupling regime, and Fano resonances in intermediate coupling regime, and exciton-plasmon polariton formation in strong coupling regime. After that, we will discuss active tuning of the coupling strengths all the way across the weak and strong coupling regime via electrical gating. Finally, we will demonstrate chiral exciton-plasmon coupling by designing chiral plasmonic lattices.