This paper presents a few examples of manipulators and micro-robots based on piezo-actuators developed during the last 4 years in the Laboratoire de Systèmes Robotiques (LSRO) at EPFL. Three working principles will be described (bender, inch-worm, inertial drives) and illustrated through examples for various applications (neurology, micro-biology, electro discharge machining, nano-material testing and assembly of carbon nanotubes). Our goal is to demonstrate that an innovative mechanical design can make it possible to realize extremely simple manipulators working in the nanometer range for applications in micro-biology and nanotechnologies.