Summary: Stored angular momentum devices such as reaction wheels and control moment gyros have been used extensively for space vehicle attitude control. They represent a potential source of actuation for vibration and shape control of large space structures where they can potentially be distributed in large numbers. The vibration characteristics of these gyroelastic vehicles are affected by the presence of stored angular momentum and, hence, so are the conditions for controllability and observability. In this paper, these conditions are derived for systems modeled as gyroelastic continua, i.e., vehicles with continuous distributions of mass, stiffness, and gyricity (stored angular momentum). The conditions are expressed in terms of the gyroelastic modes and cover the case of pointwise actuators and those modeled in a continuum fashion. A numerical example is used to show that the degree of controllability in the continuum case can be interpreted as that corresponding to the limit of a sequence of pointwise control problems. The observability conditions are developed for a general class of measurements. The concept of a gyroelastic node is introduced and related to the problem of locating sensors.