The cometary spin state and its evolution is essential to understanding the structural and physical properties of the nucleus. The detailed spin state identifies whether the nucleus is executing simple rotation about the short axis or whether it is in a dynamically excited non-principal axis rotational state as well as the parameters specifying the spin state which includes the rotation period(s), and the direction of the rotational angular momentum vector. Unfortunately, the current observational data base on cometary rotational states is limited. Space and ground based observations of comet Halley during its 1986 apparition identified it as the first cometary nucleus undergoing non-principal axis rotation. Consequent numerical studies have shown that complex rotational states should be expected for many comets with strong localized outgassing and the direction of rotational angular momentum should asymptotically evolve towards the vicinity of perihelion or aphelion directions. I will present a comparison of observational results and numerical studies of cometary spin states. I will also discuss the effects of collisions on the spin states of Kuiper Belt objects and the implications for the nuclear structure. A brief comparison will be made with cometary and asteroidal spin states.