To realize nano-scale opto-electronic circuitry, one needs to be able to excite and detect surface plasmon polaritons (SPPs) by electrical means. Tunnel junctions can excite and detect plasmons in a single step without the need for external light sources and optical elements [1-3]. In these devices, currents are directly converted to SPPs in a single step, and vice versa, at tunneling time-scales, and tunnel junctions are widely used in commercial devices. During the talk I will discuss our recent progress in the development of molecular tunnel junctions and diodes based on self-assembled monolayers (SAMs), and how we apply them as electrical excitation sources for SPPs [4-10]. By simply applying a bias between the top and bottom electrode, a tunnelling current will flow across the molecules which excites surface SPPs at the surface of the plasmonic electrode materials. Here, it is important to minimize the number of defects based on self-repair intrinsic to the self-assembly process of SAM formation [4]. Since the tunneling direction can be controlled by simply changing the chemical and supramolecular structure of the SAMs (e.g., tilt angle of the SAM via odd-even effects [10]), we have the ability to control the plasmonic properties of the devices and directionally launch plasmons (and the polarization of the emitted photons) [6]. By using molecular diodes, we achieved bias-selective SPP excitation. These plasmon sources behave as point sources whose blinking properties and photon energies can be controlled by simply changing the molecular structure giving new insights in the mechanism of charge transport [7]. Finally, by integrating two tunnel junctions with one plasmonic wave-guide, we demonstrate that the tunnel junctions are also promising as plasmon detectors with plasmon-electron coupling efficiencies of more than 1000 times higher than previous estimates based on photon out coupling rates [8]. Our results show that molecular electronics make it possible to manipulate light at the molecular length-scale and are interesting for applications in plasmonic-electronics in more general.