  Spin glasses are disordered magnetic systems that exhibit a variety of
properties that are characteristic of complex systems. After a brief review of
basic spin glass concepts, their use in areas such as computer science,
biology, and other fields will be explored. This use and its underlying basis
will be termed old complexity. Newer concepts and ideas flowing from more
recent studies of spin glasses will then be discussed, leading to a proposal
for a kind of new complexity.
