We develop rational chemical strategies to synthesize novel one-dimensional nanowire materials of transition metal silicides with precisely controlled atomic and nanoscale structures, and investigate their physical properties, and use them as nanoscale building blocks for the bottom-up assembly of integrated spintronic, photonic, and electronic nanosystems. We will report general and rational synthetic approaches to family of transition silicide nanowires and their heterostructures. Our first approach utilizes CVD of metal carbonyl-sillyl single source precursor complexes to synthesize, for example, free standing single crystal FeSi and CoSi nanowires without any catalyst seeds. We believe have observed a new nanowire growth mechanism that is generally applicable to silicide nanowire formation. We use a complementary method of chemical vapor transport for early transition metal silicide that analogous organometallic complexes do not exist. We have also developed a facile method to pattern the locations of nanowire growth. FeSi is the only transition metal Kondo insulator and the host structure for ferromagnetic semiconductor Fe_xCo_1-xSi. Controllable synthesis of the ferromagnetic semiconducting Fe_xCo_1-xSi nanowires, the investigation of the physical properties of these new silicide nanowires using electrical transport, magnetometry and X-ray spectroscopy, and their appplications will also be discussed.