Devices in a diversity of application scopes are now evolving towards miniaturization, functionalization and integration. Finely-patterned 3D micro-nanostructures are in great demand as core components in more and more devices. This keeps challenging the current micro-nanofabrication techniques. 3D femtosecond laser nanoprinting (FsLNP) is an outstanding mask-free three-dimensional additive fabrication technique with both powerful designability and high accuracy far beyond the optical diffraction limit. Based on the unique two-photon photopolymerization mechanism of 3D FsLNP, a series of highly efficient and well-functioned micro-nanodevices can be fabricated when suitable photopolymerization scheme and structure arrangement are given. In this review, we briefly introduce the technical essentials and physical fundamentals of 3D FsLNP, as well as several typical application examples.