The ALEPH vertex detector

The ALEPH Silicon Vertex Detector (VDET) is operational inside the apparatus since 1991. The novel technology of double-sided silicon strip detectors has been demonstrated a powerful tool in reconstructing vertices in 3D with LEP running at Z0 c.m. energy; some results from this running experience will be presented. Due to the VDET key role for b-tagging in the Higgs boson search at LEP200 the detector has been upgraded to improve the performance. An overall description of the VDET II will be given and the results obtained in the first run of LEP at Ecm = 131 GeV will be discussed.