IN THIS ARTICLE, AN INTRODUCTION IS PRESENTED ABOUT THE ENERGY HARVESTING TECHNOLOGIES THAT HAVE POTENTIAL FOR POWERING NANOSYSTEMS. OUR DISCUSSION MAINLY FOCUSES ON THE APPROACHES OTHER THAN THE WELL-KNOWN SOLAR CELL AND THERMOELECTRICS. WE MAINLY INTRODUCE THE PIEZOELECTRIC NANOGENERATORS DEVELOPED USING ALIGNED ZNO NANOWIRE ARRAYS. THIS IS A POTENTIAL TECHNOLOGY FOR CONVERTING MECHANICAL MOVEMENT ENERGY (SUCH AS BODY MOVEMENT, MUSCLE STRETCHING, BLOOD PRESSURE), VIBRATION ENERGY (SUCH AS ACOUSTIC /ULTRASONIC WAVE), AND HYDRAULIC ENERGY (SUCH AS FLOW OF BODY FLUID, BLOOD FLOW, CONTRACTION OF BLOOD VESSEL, DYNAMIC FLUID IN NATURE) INTO ELECTRIC ENERGY FOR SELF-POWERED NANOSYSTEMS.