This chapter describes the basic techniques employed to test optical fibre devices, using optical switches as an example. It presents common testing methods required by industry standards. In these tests, losses and other parameters, such as wavelength, will be measured. Students will become familiar with types of losses and customer requirements. Students will also learn how to use some optical testing instruments, such as an optical spectrum analyser (OSA). This chapter also presents three experimental cases to demonstrate the principles of testing a fibre optic device.