Not all that cannot be seized is an illusion! Many effective powers in nature cannot be seized, including magnetism, electricity and sound. However, they contribute to shaping the quality of human life on a daily basis, transcending health and disease as they interact with the human body. Magnetism is important for stability on earth; however, exposure of the body to magnetic fields is not inert. Such exposure has been reported to alter hormone secretion and stimulate bone formation in vivo. Its coupling with electricity provides light and heat to our planet at certain wavelengths. Yet, the infiltration of shorter or longer wavelengths can be disastrous. For instance, ultraviolet radiation can cause inflammatory skin reactions and carcinogenesis at certain levels. In addition, ionising radiation is claimed to be the driving force for the origin of power resources on earth, while human exposure to radiation is related to the world's most devastating events. On the other hand, sound, which is a mechanical wave, has been reported to affect cells at inaudible levels, causing alterations in the gene expression and cell death. All these energies as such are identified to exert physical stresses in a biological milieu especially when thresholds of exposure are exceeded. But still "hard times" have significance! Researchers have been accumulating knowledge on the biological effects of these physical stressors and their underlying mechanisms on the molecular and genetic levels, that over years they were able to achieve control over these physical stressors for the benefit of human kind. Nowadays, we see most of these energies employed in diagnosis such as magnetic resonance imaging (MRI) and ultrasound as well as in therapeutics. In our rigorous war against cancer, numerous patients have been cured from tumours by physical means such as ionising radiation, heating (RF and MW hyperthermia or ablation) or high intensity focused ultrasound (HIFU). Through the chapters of this book, the readers will get introduced to such physical stressors and their biological effects. Recent findings on molecular mechanisms will be thoroughly presented. In addition, perspectives on the modulation of these energies to achieve further therapeutic advantages will be discussed.