The following reprint aims to examine the innovative energy-harvesting (EH) technologies that are facilitating the advancement of the Internet of Things (IoT) and Wireless Sensor Networks (WSNs) towards enhanced autonomy and sustainability. As the demand for efficient, low-power IoT devices increases, so too does the necessity for sophisticated EH solutions capable of converting ambient energy sources, including solar, thermal, vibrational, and radio frequency, into usable electrical power. This compilation examines the innovative materials, advanced transduction mechanisms, and sophisticated energy management circuits that are propelling these advancements. By harnessing ambient energy, these technologies are reducing reliance on traditional power sources, thereby enhancing the efficiency and sustainability of WSNs. Furthermore, the research presented in this collection emphasizes the minimization of the energy consumption of wireless sensor nodes, highlighting innovations that contribute to the development of long-lasting, self-sufficient sensor networks. This reprint offers readers a comprehensive overview of the latest trends and breakthroughs in the field, providing valuable insights into the future of sustainable IoT and WSN applications.