Semiconductor nanorods are an exciting material for optical applications because their absorption and emission properties can be tuned by the nanorods size, aspect ratio, and composition. In this chapter we will discuss the in detail the electronic level structure and the time dynamics of the carrier relaxation processes which determine the optical behavior of nanorods. Experiments on single nanorods of single and heterostructured materials will be reviewed that demonstrate, for example, polarized and directional emission, and tuning of the emission wavelength via the nanorod size or the Stark-effect. Furthermore coupling and collective effects in nanorod arrays will be discussed and we will highlight some promising results towards practical applications of nanorods in light emitting or lasing devices.