We present an integrated composite right/left handed transmission line (CRLH-TL) phase shifter analogically controlled by means of a MEMS series capacitor. The device is based on coplanar waveguide (CPW) technology and operates at a central frequency of 18 GHz. An accurate and physical circuit model including parasitics inherent to this MEMS realization is presented. We describe the method used to design the presented structure, which consists in a mixed approach using the developed circuit model and full-wave simulations. The MEMS-controlled CRLH-TL has been fabricated and characterized, showing good agreement with predicted performances.