Non-native species (NNS) (sometimes referred to as non-indigenous species) are organisms that are found outwith their natural range as a result of human action. Many coexist with native species with little or no impact, but some can alter the local ecology by smothering and ultimately displacing native species and are referred to as invasive non-native species (INNS). The Non-native species assessment is not based on any established Scotland-wide monitoring programme but rather on incidental reports and some local monitoring programmes. It uses the methods agreed by the Water Framework Directive Technical Advice Group – Alien Species Group. The Case study: Marine non-native species monitoring in the Orkney Islands is an example of a well-established monitoring programme within a single SMR that provides evidence of any spread of NNS within the Region as well as an indication of new arrivals. The Case study: Carpet sea squirt reports on the occurrence and spread of this INNS and the efforts put in place to minimise its impact. It also serves as a good example of the importance to maintain high levels of vigilance and the need for the capacity to be able to respond quickly to such events.