At very small scales, electric and magnetic field effects, such as dielectrophoresis and electro-osmosis are gaining greater focus as important tools in flow control, and magneto-electro-micro-fluidics is increasingly viewed as one of the most promising techniques for separating, controlling, and manipulating fine particles, cells, and micro-organisms in flowing suspensions. The issue is gaining in magnitude as sophisticated micro-fabrication technologies make miniaturization of a range of analytical devices possible, all requiring effective actuation mechanisms. Effective and rapid mixing of liquids in small scale devices is essential in many applications, such as hand-held pollution monitoring devices, drug delivery, DNA analysis and sequencing, pheromone synthesis in micro bio-reactors, and biological and chemical agent detection. However, mixing in micro-devices is a challenge as low Reynolds number flows encountered in these systems are in general not turbulent, and diffusion dominates mixing processes. Improving the efficiency of mixing through diffusion alone in the absence of turbulence is impractical. For instance, the diffusion coefficients of large molecules such as proteins and DNA are of the order of and even smaller. Hence, the mixing time can be prohibitively long, not to speak of the mixing length. A highly efficient fast micro-level mixer will greatly benefit a number of critical applications, such as immunological studies, DNA hybridation, and cytometric analysis. In this context, flow manipulation through judicious use of magnetic and electric fields or with actuators and internal micro-pumps becomes a central issue in applications. It should be noted that the bulk motion of electrolyte solutions driven by electric fields, electro-osmotic flows, requires large electrostatic potentials. In contrast, magnetic field driven effects do not, and may be preferable in some applications.