 This video was produced in collaboration with the International Society for Stem Cell Research, ISSCR. Our bodies are comprised of more than 200 types of cells that protect us from invaders that just our food detoxify our blood, preserve memories, and much more. Think of our bodies as an extremely complex construction project made from hundreds of parts built from trillions of cells. How are all of the parts formed, correctly assembled during construction and maintained as we grow old? Amazingly, all of the different types of cells in the body are derived from a small group of versatile master builder stem cells called pluripotent stem cells, which can generate any type of tissue or cell in the body, a skin cell, brain cell, or a heart cell. In the earliest stages of the construction project, embryonic development, pluripotent stem cells are clustered in a microscopic mass smaller than the size of the dot over an eye, called a blastocyst. Alas, these pluripotent stem cells only exist for a few days. By the time we are born, they are long gone, but they are critical for proper construction of the body plan. After we're born, our bodies can be maintained and repaired by tissue-specific adult stem cells that remain in our bodies throughout life. Tissue-specific stem cells are derived from the master builder pluripotent cells and are responsible for our body's ability to repair itself after injury, such as broken bone or a skinned knee, and therefore act as the builders, each of which is responsible for repairing a specific type of tissue. Some but not all tissues have specialized self-repair tools to fix themselves when they are damaged, from large or small injuries, like tiny muscle tears from a few hours of the gym. When the tissue is damaged, self-repair mechanisms kick in. Muscle stem cells fix the torn muscle fibers, and skin stem cells repair dead skin after a sunburn. But each tissue can only be repaired by its dedicated tissue stem cell. Muscle stem cells cannot repair new skin, and skin stem cells can't repair new muscle fibers. The discovery of stem cells has opened a new frontier known as regenerative medicine, harnessing the natural repairability of stem cells. This new form of medicine includes the use of stem cells to model diseases, test drug effects, and generate cell types or tissues in a dish for transplant into patients. Regenerative approaches may use tissue stem cells, harnessing the patient's own stem cells, boosting their innate repair abilities, or introducing tissue-specific stem cells from a donor. It may also involve using pluripotent master builders stem cells, which can be derived from two sources, ethically generated, excess blastocysts from in vitro fertilization donated with the informed consent of the donor, or through a technique that reprograms adult to become pluripotent, a process that produces induced pluripotent stem cells, IPS cells. The generation of induced pluripotent stem cells was made possible when scientists identified the genes that control the stemness of pluripotent master builder stem cells. By isolating these genes and then introducing them into non-stem cells, they reprogram them into a pluripotent stem cell state, in which they are now able to develop into any cell type. Stem cell therapies hold tremendous potential for medical research and the development of new treatments for some of the world's most devastating diseases. Because the field of stem cell research is so new, it is critical to explore all avenues of stem cell research from IPS cells, pluripotent, to tissue-specific stem cells, including fetal-derived stem cells. For this reason, California's Proposition 71 was written to be agnostic as to the stem cell type funded. Data-driven research must determine which cell type is the best, safe, and effective therapy. As we build on the progress that California's Proposition 71 and the funding agency it created the California Institute for Regenerative Medicine have enabled, we must keep the momentum going, because we still have much to learn. Only with continued support for biomedical research can we increase our understanding of stem cells in the laboratory and develop meaningful treatments that change patients' lives. To learn more about stem cell biology and their potential impact on human health, check out the ISSCR's A Closer Look at Stem Cells.