"The biggest little molecules in Nature"

This colloquium will discuss recent theoretical predictions and experimental confirmation of two unusual classes of ultra-long-range molecules. One class involves a highly-excited Rydberg electron that manages to bind a distant ground state atom at thousands of Bohr radii. The other class involves the bizarre Efimov effect for three or four ground state atoms with resonant interactions. Implications for the behavior of ultracold quantum gases will be addressed.