Harnessing energy from human motion has the potential to emerge as a viable and eco-friendly energy solution for emerging portable electronics and sensors. Ambient energy sources can be classified as energy reservoirs, power delivery systems, or energy harvesting techniques, and they can enable wireless or portable devices to function without the use of batteries. Nanogenerators are being investigated for harvesting numerous types of energy that surround us in our daily lives, such as vibrational energy, human body motion, heat, wind energy, solar energy, blue energy, thermoelectric energy, etc. To boost the output power of nanogenerators, researchers around the world have proposed hybrid nanogenerators with numerous and unique designs that use a combination of more than one of the following types: pyroelectric, triboelectric, piezoelectric, thermoelectric, and other nanogenerators. Hybridization of nanogenerators has been found to be a viable way for mechanical energy harvesting with better performance that may be employed for a wide range of applications in large-scale operations. This book chapter goes into detail on many types of nanogenerators that harvest energy from their surroundings, such as PENG, TENG, thermal, electromagnetic, pyroelectric, and their hybrid nanogenerators. The primary focus is on the fundamental working mechanisms of the aforementioned nanogenerators and the effect of nanoengineering, nanomaterials, and surface modifications in energy harvesting. © 2025 Elsevier Inc. All rights reserved.