Lithium-ion batteries are widely used for mobile devices such as smartphones and laptops, but for new applications such as electric vehicles it is necessary to develop electrode materials with higher energy density, longer cycle life, and lower cost. Silicon is a particularly attractive high-capacity anode material, but large volume changes during lithiation/delithiation result in mechanical degradation and fast capacity decay. In this chapter, the development of Si NWs and other one-dimensional Si nanostructures for Li-ion battery anodes is presented. One-dimensional Si nanostructures show improved performance as anodes because (i) they can withstand volume changes without fracture, (ii) they can remain electrically connected to the current collector during cycling, and (iii) they can be engineered for stable solid electrolyte interphase formation. In addition to electrochemical performance, this chapter also discusses in situ studies that have revealed fundamental reaction and degradation mechanisms at the nanoscale. Finally, several other NW-based electrode materials are briefly discussed. Overall, NW-based electrode architectures show great promise for Li-ion batteries with improved performance.