Silicon nanowires (SiNWs, diameter greater than or equal to 5 nm, and length similar to mum) have been fabricated with metal- and SiO2-catalyses assisted by laser ablation. In the catalytic growth of single-crystalline SiNWs by pure metal catalysts (Fe, Ru, and Pr), Si {111} is found to be the most stable plane and wire growth axis is along <111>. The growth mechanism follows a vapor-liquid-solid process, and the synthesized SiNWs typically have metal-tips composed of metal and Si, such as FeSi2, RuSi3, and PrSi4, respectively. In sharp contrast, a crystalline growth axis of <111> and a wire growth axis of <112> are the result in the SiNWs catalyzed by SiO2. Besides, the SiO2-catalytic SiNWs generally have no tips at the wire ends. Distinctive growth mechanisms resulting from metal- and SiO2-catalyses will be discussed. Pressure effect on the longitudinal and transverse growing rates in the fabrication of SiNWs has been examined.