These guidelines provide best practices for the measurement of organotin compounds in biota for monitoring programmes. Target compounds include tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) as well as triphenyltin (TPhT), diphenyltin (DPhT), and monophenyltin (MPhT). The bivalve Mytilus edulis can be a suitable target species for the monitoring of organotins. Sampling strategy as well as transportation and storage are important for the final quality of the data. Handling and pretreatment of the samples is also discussed. Several analytical methods can be used for the determination of organotin compounds. Critical steps, such as extraction and derivatization of the determinants, are discussed, followed by descriptions of the analytical detection techniques. Emphasis is placed on analytical quality control and quality assurance. Published Refereed Current 14.1 Standard Operating Procedure Guide