Semiconductors have played an important role in the development of information and communications technology, solar cells, solid state lighting.  Nanowires are considered as building blocks for the next generation electronics and optoelectronics.  In this talk, I will introduce the importance of nanowires and their potential applications and discuss about how these nanowires can be synthesized and how the shape, size and composition of the nanowires influence their structural and optical properties. I will present results on axial and radial heterostructures and how one can engineer the optical properties to obtain high performance optoelectronic devices such as lasers, THz detectors, solar cells.  Future prospects of the semiconductor nanowires will be discussed.