Plasmonic nanoantennas allow the efficient conversion of impinging optical radiation from the far-field into confined, strongly enhanced fields at the nanoscale or, by reciprocity, the coupling of localized optical sources to far-field radiation. Recent advances in nanofabrication, near-field measurement techniques and characterization, as well as in theoretical modeling, have led to a rapid growth of interest in these nanodevices for a wide range of applications, including biological and chemical sensing and detection, efficient light emitters, optical imaging, communications within nanophotonic chips, nanoscale nonlinear optics, energy harvesting and thermotherapy. In particular, nonlinear optical activity and quantum interaction with light, which are typically weak over small volumes, can be dramatically enhanced owing to the resonant interaction of light in subwavelength nanoantennas, based on the strong field enhancement sustained by plasmonic effects. In this chapter, we provide an overview of the recent design, fabrication, and characterization efforts on plasmonic antennas. We show that it is possible to apply familiar radio-frequency concepts to model and design optical nanoantennas, and we use these powerful design tools to predict the linear and nonlinear response of plasmonic nanoantennas and model nanodevice designs for all-optical communications and signal processing.