Progress in ZnO thin films and nanostructures for the acoustic wave microfluidic and sensing applications are reviewed in this chapter. ZnO thin films with good piezoelectric properties possess large electromechanical coupling coefficients and can be fabricated for the surface acoustic wave (SAW) and film-bulk acoustic resonator (FBAR) devices with a good acoustic performance. The SAWs can be excited to mix, stream, pump, eject, and atomize the liquid, and precision sensing can be performed using SAWs and FBARs. Therefore, the ZnO SAW devices are attractive to be integrated into a labon-chip system where the SAWs can transport bio-fluids to the desired area, mix the extracted DNA or proteins, and detect the changes of the signals using SAWs or FBARs. The ZnO SAW and FBAR devices in combination with different sensing layers could also be used to successfully detect gas, UV light, and biochemicals with remarkable sensitivities. 5.1 INTRODUCTION Zinc oxide (ZnO) is a binary compound via a covalent bonding between the transition-metal zinc atom and oxygen atom. ZnO thin films and nanostructures are multifunctional materials, which have attracted much attention from as early as 1930s until today due to various fundamental electronic, years, the development of new growth technologies of ZnO thin films and nanostructures and their new applications has renewed lots of interest on investigation of their growth mechanism, band structures, excitons, and deep centers in luminescence, nonlinear optics, and UV lasing [8,9]. With in-depth understanding of the semiconducting, optical, electronic, piezoelectric, and pyroelectric properties, ZnO has now been widely applied for microfluidics, These immense applications also have boosted the extensive researches on the fundamentals and growth techniques of the ZnO-based materials. typically at micron and submicron dimensions in a miniaturized system and the corresponding technologies for such systems. This multidisciplinary technology is comprehensively based on physics, nanotechnology, biotech-ZnO Thin Films and Nanostructures for Acoustic 197 the developments of the inkjet print-heads, DNA chips, and lab-on-a-chip is conveniently handled through generating, transporting, separating, consumption, high-throughput, compactness, high sensitivity, fast response, at microscale has been supported with the urgent needs from healthcare, medical research, life science, drug-development sectors. However, the and phenomena become dominant at a microscale level, such as capillary forces, surface roughness and undesired chemical interactions. These may be