RF-MEMS filters such as Bulk-Acoustic-Wave (BAW) filters are determined to replace conventional RF-filters in mobile communication as they have demonstrated performance and size advantages and can be manufactured at very low costs. Key performance parameters and requirements are discussed in detail. Two different approaches for RF-MEMS filters are reviewed and compared: Electric field driven MEMS-resonators and piezoelectric MEMS resonators. State-of-the-art RF-MEMS filters based on BAW resonators are presented.