The spectacular growth in MOEMS interest is highlighted by the involvement of R&D centres and industrial companies. A lot of application fields offer large opportunities for Micro-Opto-Electro- Mechanical Systems (MOEMS): optical communications (switches, cross- connect matrix, DWDM systems ...), digital image processing, adaptive optics... but also industrial maintenance, environment, medicine,... After general ideas on MEMS and MOEMS, this paper presents the main application fields for MOEMS and a few outstanding devices are presented to illustrate the recent developments. Then the work of LETI in MOEMS is presented. Some devices are fabrication with MEMS technologies such as tunable Fabry-Perot interferometers for DWDM telecommunications or 2D micro-scanners for obstacle detection. But a more specific technology has also been developed by LETI, resulting in devices made of silica such as 1D micro-scanners for obstacle detection. Moreover some devices are constituted of micro-mechanical structures combined with Integrated Optics: micro-switches for protection applications and network reconfiguration in optical communications, micro-vibration sensor for surveillance of rotating machines in electrical generators.