A dedicated evaluation and qualification campaign has been performed on several optical COTS components in order to use them on ESA’s SMOS mission. The evaluation phase consisted of a set of critical tests and analyses and led to the selection of the flight lot component. After selection of the components, one lot of each component has been qualified for the SMOS mission. <p> </p>The overall approach is presented together with a summary of all activities performed. The whole task has been handled in a joint effort between ESA, EADS CASA Espacio (prime contractor), Contraves Space AG (MOHA subsystem), TECNOLOGICA SA (component qualification experts) and the respective manufacturers, each party providing their specific know-how. Test results are presented and the issues discovered and lessons learned are addressed. Special emphasis is given to particular tests for which dedicated setups had to be designed due to the unavailability of standard equipment.