The determination of the dose of inhaled aerosol particles in animal subjects is not a trivial exercise. In its simplest form, the dose is the amount (particle number, mass or other relevant metric) that deposits in the respiratory tract. The amount deposited will depend on the aerosol particle sizes (e.g. the aerodynamic diameter size distribution), the duration of exposure, the exposure system's delivery efficiency, the subject's ventilation rate, the species and strain, and other factors. Similarly, species differences in the clearance rates of deposited particles will influence the time integrated particle doses. In practice, particle doses are estimated using mathematical models, previous experimental dosimetry data, tracers of the inhaled particles and biomarkers of exposure. With care, desired aerosol doses can be achieved and documented.