Neutral ytterbium (YbI) and singly ionized ytterbium (YbII) is widely used in experiments in quantum optics, metrology and quantum information science. We report on the investigation of isotope selective two-photon-ionization of YbI that allows for efficient loading of ion traps with YbII. Results are presented on two-colour (399 nm and 369 nm) and single-colour (399 nm) photoionization and their efficiency is compared to electron impact ionization. Nearly deterministic loading of a desired number of YbII ions into a linear Paul trap is demonstrated.