Gold and silver nanorods and, in the case of silver, nanowires, have been prepared in our laboratory in a seed-mediated growth procedure that can be done in water at room temperature. Shape control is provided by a cationic surfactant in solution. High-resolution transmission electron microscopy, selected area electron diffraction, and screening of reaction conditions have all led to a proposed reaction mechanism whereby the counterion to the cationic surfactant adsorbs preferentially to certain crystal faces of the growing nanomaterial to control its overall shape. The surface chemistry of the nanorods can be tuned for to change the overall charge or hydrophobicity of the nanoparticles. The optical properties of the nanomaterials depend on aspect ratio, and the longitudinal plasmon bands can be tuned from the visible into the near-infrared. The metal nanorods also Rayleigh-scatter light well, and in addition are good substrates for surface-enhanced Raman scattering.