The methods used to count radioactive disintegration rates, determine specific activity, and quantify radiolabeled agrochemical and its transformation products at various analytical steps are discussed in this chapter. Liquid scintillation counting, LSC, is the most sensitive method for the quantification of all forms of radioactivity. In the 14C-radiolabeled samples, LSC detects and counts the nuclear disintegration events by capturing and registering the photons produced from the emitting β− particles. The detection and quantification limits of radioactivity in test samples are established using Currie’s working expressions. Specific activity of a radiolabeled compound is determined by gravimetric as well as spectroscopic methods. Both combustion analysis and extraction methods are used to determine total radioactive residue in test samples. The radioactive components in sample extracts are separated and quantified by thin-layer chromatography, TLC, and high performance liquid chromatography, HPLC. The degradation rates of agrochemicals in environmental media are calculated by SFO and PestDF kinetic models. PestDF tool is employed to determine representative half-life values of agrochemicals in soil and aquatic transformation studies. Regulatory agencies use these half-life values in the risk assessment and exposure modeling programs.