Cooperation and conflict are universal themes that arise when considering how entities at various levels of organization interact. This is particularly true in biology, from atoms interacting within a molecule, molecules interacting within a cell, or cells interacting within a multicellular organism, individuals interacting within groups, disease organisms interacting within their host, or nations interacting with one another. We will explore how the concepts of game theory apply at the biochemical, cellular and organismal levels to explore how groups of entities at these various levels interact, and how groups transition to individuals. All along the way we will discuss a lot of biology and see how biologists apply what they know to new problems. McPeek.