Herein we describe the syntheses of high-quality PbS and CdS nanowires by the solution-liquid-solid (SLS) mechanism from single-source precursors. The SLS synthesis of nanowires offers several advantages over other methods, including purposeful control of nanowire mean diameters, narrow diameter distributions, small diameters in the quantumconfinement regime, control of surface passivation, nanowire solubility, and ease of implementation.[1] However, although SLS growth has been applied to a wide range of II-VI, [2] III-V, [3] and IV-VI [4] nanowire compositions, the method is not yet generally applicable, as each new composition requires extensive trial-and-error experimentation to identify appropriate precursors and reaction conditions. Our prior work has employed separate metallic-element and nonmetallic-element precursors to synthesize high-quality, compound-semiconductor nanowires. [2a,d, 3d,g] Finding dual precursors with appropriately balanced reactivities has often been a primary origin of the extensive empirical experimentation required to develop a given, successful SLS nanowire synthesis. In several cases, such as for metal-sulfide semiconductors, the dualprecursor SLS approach has failed to produce highly crystalline, diameter-controlled nanowires (see Figure S1 in the Supporting Information).We now report that the use of single-source precursors, in which the metallic and nonmetallic semiconductor constituents are combined in a single molecule, solves the reactivitybalance problem, resulting in the successful SLS growth of PbS and CdS nanowires. Therefore, the single-source approach has the potential to greatly extend the generality of the SLS method for semiconductor-nanowire synthesis. As single-source precursors have been extensively developed for use in the MOCVD growth of thin films, [5] suitable precursors for the SLS growth of many new nanowire compositions are likely already available.Semiconductor nanowires have drawn increasing interest for their potential applications in electronic and photonic devices [6] such as field-effect transistors, light-emitting diodes, logic gates, lasers, waveguides, and solar cells. Multipleexciton generation was recently discovered in nanocrystals of PbS and PbSe. [7] Specifically, up to four excitons (quantum yield up to 430 %) were produced by absorption of a single photon in PbS nanocrystals.[7a] Although the ultrafast nonradiative Auger recombination of multiexcitons prevents the carriers from being harvested so far, this obstacle may be overcome by using elongated nanostructures, such as nanorods and nanowires.[8] If the rate of Auger recombination is significantly slower in 1D nanostructures, the efficiency of photovoltaic energy conversion might be greatly enhanced. Additionally, PbS has a relatively large exciton Bohr radius of 20 nm, [9] which makes it one of the ideal candidates for investigating quantum-confinement effects in relatively large nanostructures. The high quality of the PbS nanowires reported here enabled observation of discrete excito...