Lipids are a broad group of organic compounds that include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, phospholipids, and others. They are essential to many body functions and serve as the building blocks for all living cells. Lipids are characterized by their solubility in nonpolar solvents and insolubility in water. They are energy-rich organic molecules that provide energy for different life processes. Lipids have several functions in the body, including storing energy, signaling, and acting as structural components of cell membranes. They also help with moving and storing energy, absorbing vitamins, and making hormones. Lipids are in every cell in the body and are part of the cell membrane, which gives cells structure and allows substances to go in and out of cells. Some lipids are harmful when present in excess, and a lipid panel can tell if someone has normal levels. Lipids have applications in the cosmetic and food industries, and in nanotechnology.