The ability to control and manipulate small objects is essential in studying many microscopic phenomena, from colloidal physics to molecular biology, and more recently, nanophotonics. Optical tweezers offer a unique non-contact approach to control the position and orientation of microscopic particles. In this lecture, I will introduce the development of optical tweezers with emphasis on the underlying physics of optical trapping, especially the interactions of light with plasmonic nanoparticles. Various designs of optical trapping systems will be discussed, as well as the issues involved in constructing and using optical tweezers. In particular, I will describe holographic optical tweezers that use structured optical fields to tailor the optical trapping of specific plasmonic nanostructures. A number of the applications of optical tweezers in life sciences and colloidal physics will also be discussed.