A principal challenge facing nanotechnology is consistently producing well-defined features much smaller than the wavelength of visible light. We find that the remarkably sharp threshold for femtosecond laser-induced material damage enables nanomachining with unprecedented precision and versatility, allowing highly reproducible machining of structures with nanoscale features. Using this methodology, we demonstrate, in glass, surface trenches that are only tens of nanometers in width but micron in depth, sub-surface channels that are hundreds nanometers in diameter, tens of microns deep, and hundreds microns in length, and 3D microstructures such as cantilevers. Furthermore, we demonstrate reproducible nanometer scale features in mixed and amorphous materials that differ significantly from glass, such as gold and onion cells. This technique is versatile, not material specific, and has potentially broad applications for MEMS construction and design, high density microelectronics, nanofluidics, material science, and optical memory.