Dielectrophoresis (DEP) is a powerful tool that has been widely used to manipulate (e.g., focus, trap, concentrate, and sort) particles and cells in microfluidic devices. Traditional electrode-based DEP (eDEP) arises from the non-uniform high-frequency AC electric field between pairs of electrodes that are fabricated within a microchannel. This method suffers from the problems of fabrication complexity and electrode fouling etc. Such problems are significantly mitigated in the so-called insulator-based DEP (iDEP) devices, where both AC and DC electric fields can be applied through the electrodes that are positioned virtually outside a microchannel. However, in-channel insulating obstacles such as hurdles, posts, and ridges are required to create the electric field gradients. The locally amplified electric field around these micro-obstacles may cause adverse effects on both the sample and the device due to potential Joule heating and particle clogging issues. Our group has recently developed a new method that exploits the curvature of insulating walls for a diverse electrical control of particle and cell motions in microfluidic devices. Due to the variation in path length for electric current, the electric field becomes inherently non-uniform within a microchannel corner. Thus induced DEP can generate both a crossstream and a counter-stream particle motion, which are second-order function of the electric field and are superimposed to the linear electrokinetic motion for flexible particle manipulations. In this talk I will present our recent results on the dielectrophoretic focusing, trapping, concentration, and separation of particles and cells in curved microchannels and microfluidic reservoirs with applications to lab-on-a-chip systems.