Electrons in One dimension-Spin-Charge Separation and Localization. The behavior of electrons in a solid-state environment is often qualitatively modified from their vacuum properties due to Coulomb interaction. The low energy properties of such interacting systems are described in terms of dressed elementary excitations known as quasi-particles which interact only weakly among themselves. In two and three-dimensional disordered metals quasi-particles bear a strong resemblance to free electrons. They each carry a charge e and spin half and most importantly, their excitation spectrum, which for non-interacting electrons is simply determined by the underlying band mass m, is only slightly modified by the Coulomb interaction. However, the underlying quasi-particles in a one-dimensional metal, know as a Luttinger-liquid, are utterly different from free electrons. Here, for example, the spin and charge degrees of freedom completely decouple and can be separately excited. Using momentum and energy resolved tunneling between two closely situated parallel wires we have measured the collective excitation spectrum of electrons confined to one-dimension. At high electron densities, spin-charge separation is clearly observed. At low electron densities the system abruptly looses translation invariance and becomes localized. Our measurements indicate that the localization length corresponds to the inter-electron spacing.