This study examines the enhancement of heat pipe thermal performance through the employment of composite wicks. Wicks were fabricated from a biporous structure comprised of fine nickel metal powders sintered onto layers of coarse pore copper mesh. Wick structures were designed to explore the effects of both enhanced evaporation heat transfer at the liquid/vapor interface and the extension of the capillary limit. A number of composite wick heat pipe configurations were fabricated and tested to assess performance improvements in comparison to conventional designs. Horizontal, gravity-assisted, and against-gravity tests were conducted to determine whether these designs were orientation-dependent. At various heat inputs, some configurations achieved thermal performance levels greater than three times higher than those of conventional heat pipes. During against-gravity tests, virtually all composite designs exhibited improved performance over the conventional heat pipe at all heat inputs. These results clearly demonstrated that significant improvements in heat pipe performance were achieved through composite wick design.