Precession as a probe of the neutron star interior

Strong evidence that some neutron stars precess (nutate) with long periods (∼1 yr) challenges our current understanding of the neutron star interior. I describe how neutron star precession can be used to constrain the state of the interior in a new way. I argue that the standard picture of the outer core, in which superfluid neutrons coexist with type II, superconducting protons, requires revision. One possible resolution is that the protons are not type II, but type I. Another possibility is that the neutrons are normal in the outer core. I conclude with a brief discussion of the implications for detectable gravitational wave emission from millisecond pulsars. Much of the work described here was supported by the National Science Foundation under Grant AST-00098728.