Optical antennas or plasmonic antennas are nanoscale metallic structures which act as effective receivers, transmitters and receivers of visible light. Different canonical nanostructures such as metallic nanorings [1], nanorods [2], nanowires [3], dimers [4] or nanoshells [5] are commonly used as optical nanoantennas. These nanoatennas show the ability to focus electromagnetic radiation into tiny spots of nanometer-scale dimensions allowing for more effective field-enhanced visible spectroscopies such as in surface-enhanced Raman spectroscopy (SERS) or in SEIRA. We will address here the optical response of these nanoantennas in a variety of configurations such as in active devices, in scattering-type Near-field Optical Microscopy, or in scanning transmission electron microscopy, among others.