Nanodosimetry (ND) is inspired by modern radiation therapy (RT) technologies and the needs of molecular and micro radiobiology. ND aims to detect radiation dose absorbed by nanovolumes. Modern RT provides extremely high absorbed dose gradients within a patient’s body. Therefore, to detect a distribution of the dose, a linear size of the detector should fit the scale from 100 nm to a couple of micrometres. Since RT aims to destroy DNA, where a single unit is on the nanometer scale, ND is of radiobiological importance. If the high dose gradient is provided, a thin film detector or a thin surface layer of the solid material could be used for dosimetry. If 3D nanovolume is of the interest, the nano-dotted/particle-based detector can be used. Weak electron near threshold photoemission (PE) is considered for readout of the dose absorbed by the nano-sized detector. The application of PE for ND is related to the nanometric mean free path of the emitting electron. PVDF nanofilms, the surface of a crystalline Si, PbS nanodots and diamond nanoparticles are considered for ND.