This chapter describes the many forms of modern creationist movements. These include the “young Earth creationists” (YECs), who adhere to the notion that the world is around 6000 years old, based largely on the calculations of seventeenth-century Archbishop James Ussher, who calculated the date of creation to October 23, 4004 BCE, based on computations of generations of the lives of Biblical characters and cross-referenced to known historical dates at that time. Thus, the axiom of YEC thought is that all other activities must fit within those 6000 years, and much of their research and publications attempt to fit everything into that window. Several politically active YEC groups are described here. In addition, several groups propound the idea that the strict and literal designation of 6000 years may be metaphorical or astronomically variable. These are the “old-Earth creationists” (OECs), who maintain more flexible histories, which uphold different versions of OECs. Attempts to codify creationism as a scientific explanation of the Earth inspired “creation science” or “scientific creationism,” whose proponents attempted to place it into the scientific curricula in schools. These were the subject of several legal fights that eventually led to their defeat in the courts.