 While most of the philosophical literature about molecular structure and geometry is about bonding, there are a number of important questions concerning the notion of molecular structure itself. The first issue involves the correct definition of molecular structure. Textbooks typically describe a molecule’s structure as the equilibrium position of its atoms. Water’s structure is thus characterized by 104.5º angles between the hydrogen atoms and the oxygen atom. But this is a problematic notion because molecules are not static entities. Atoms are constantly in motion, moving in ways that we might describe as bending, twisting, rocking, and scissoring. Bader therefore argues that we should think of molecular structure as the topology of bond paths, or the relationships between the atoms that are preserved by continuous transformations (Bader 1991).