This book provides a comprehensive introduction to multiferroic (MF) and magnetoelectric (ME) materials, with a strong emphasis on their structural characteristics and a primary focus on emerging, non-toxic variants. It highlights green synthesis techniques and explores a broad spectrum of energy harvesting applications. In-depth coverage is given to the use of these materials in cutting-edge applications such as spintronic, photovoltaics, photocatalysis, sensors, gyrators, gradiometers, transducers, and memory storage devices. Special attention is paid to eco-friendly, lead-free MF-based smart materials, which are increasingly utilized as sensors and actuators in nano/micro-electromechanical systems (N/MEMS). ME-coupling-based N/MEMS devices, in particular, demonstrate high-quality factors and compatibility with radio frequency-integrated circuits (RFICs). The book also discusses the biomedical potential of non-toxic ME antennas, especially in neurological applications. Furthermore, it classifies ME-MF-based technologies into three categories based on the nature of ME coupling: direct, converse, and combined. Concluding with a critical analysis of sustainable, non-toxic, and commercially viable ME-MF technologies, the book also briefly introduces advanced and emerging concepts such as quantum electromagnets, quantum criticality, and cosmic string laboratory simulations.