Sea lice are a naturally occurring marine parasite of fish. Over 500 species can be found on most fish types worldwide. Two main species affect salmon in Ireland, Lepeophtheirus salmonis (the salmon louse) and Caligus elongatus. Sea lice monitoring of finfish sites have taken place on licenced finfish aquaculture around Ireland. This sea lice monitoring programme has been in operation since 1991 and is widely regarded as international best practice. The purpose of the monitoring programme has been to evaluate the levels of sea lice on growing finfish so that information on a control strategy can be provided, by advising treatment if necessary. All stocks of fish have been inspected by Marine Institute Inspectors on 14 occasions throughout the year. The Marine Institute has carried out regular inspections of sea lice levels on all fish farms in Ireland in accordance with the Department of Agriculture, Food and the Marine sea lice Monitoring Protocol (2000) and Strategy (2008). Results from the programme have been reported each month to stakeholders and all the data has been published on an annual basis. Data complete for each year since 1991.