The present chapter provides a description of internal dose estimates following tritium intake through the analysis of biokinetic models, dosimetric models and bioassay results. Assessing the committed effective dose received as a result of taking tritium into the body is done in two steps. First, a biokinetic model describing the behavior of the tritiated compounds after incorporation into the human body is used to predict where the tritium will go in the body and how it will be removed from it. The compartment model of the retention kinetics of tritiated water (HTO) and organically bound tritium (OBT) recommended by ICRP(International Commission on Radiological Protection) publications is examined throughout the chapter for the purpose of investigating the importance of the main metabolic routes. Biokinetic models of different tritium compounds are analyzed, among which gaseous tritium (HT, DT, and T2), HTO, OBT and special tritium compounds. Second, a dosimetric model is used to calculate how much tritium will decay while it is in the various organs and tissues of the body and how much of the energy from the beta particles will be absorbed by the body. This allows the evaluation of the dose resulting from the intake of tritium. In the present chapter, the ICRP methodology for calculating the internal absorbed dose from inhaled, ingested and skin-absorbed tritium will be presented. Finally, the established way of calculating the amount of activity deposited within the body is by bioassay samples, i.e. by measurements of urinary excretion. In fact, both the amount of tritium retained in excreta and the committed effective dose are directly related to the intake: therefore bioassay measurements are used to determine the dose received. A worked example is also provided to help the reader understand how the dose received can be determined from bioassay results ©2013 Nova Science Publishers, Inc. All rights reserved.