The ISO is a former International Sailing Federation (ISAF) class of two-person sailing dinghy with a single trapeze and an asymmetric spinnaker. The ISO was designed in 1993 by Ian Howlett and John Caig. The boat has a fully battened mainsail, jib and an asymmetric spinnaker.
The name ISO reflects a feature of the design that allows different sized crews to compete on an equal basis. This is achieved by a crew weight equalisation system consisting of removable wings. The wings may not be used if the trapezing crew weighs more than 78kg (to equalise righting moment) and must be used if the combined helm and crew weight is less than 135kg (to equalise weight in the boat). If neither of these mandatory rules apply the crew may choose whether or not to use wings but may not change this decision during a race series.
Around 700 boats were built with sail numbers starting at 501. The ISO is designed to be a relatively easy boat to sail for its performance level. It belongs to the racing skiff category. In the UK the ISO Class Association is affiliated to the Royal Yachting Association (RYA).