There is a worldwide race to find materials with high thermoelectric (TE) efficiency to convert waste heat in consumer electronics and server farms to useful energy. Despite several decades of development, the state-of-the-art TE materials are not sufficiently efficient to deliver viable technology platform for energy harvesting from consumers electronics or on-chip cooling of CMOS-based devices. The efficiency of a TE material is defined by a dimensionless figure of merit ZT which is proportional to the Seebeck coefficient (S) and the electrical conductance (G) and inversely proportional to the thermal conductance κ. Therefore low-κ, high-G and high-S materials are needed. This is constrained by the interdependency of G, S and κ. Consequently, the world record ZT is about unity at room temperature in inorganic materials which are toxic and their global supply is limited. To develop high-performance TE devices, simultaneous engineering of electron and phonon transport through nanostructured TE materials is needed. In molecular scale junctions, electrons behave phase coherently and can mediate long-range phase-coherent tunneling even at room temperature. This creates the possibility of engineering quantum interference in these junctions for thermoelectricity. In this talk, I will discuss strategies to improve the efficiency of TE materials. This includes utilising quantum interference to enhance electrical conductance and Seebeck coefficient and phonon interference to suppress thermal conductance in molecular scale junctions.