  A mean field type control system is a dynamical system in the Wasserstein
space describing an evolution of a large population of agents with mean-field
interaction under a control of a unique decision maker. We develop the
viability theorem for the mean field type control system. To this end we
introduce a set of tangent elements to the given set of probabilities. Each
tangent element is a distribution on the tangent bundle of the phase space. The
viability theorem for mean field type control systems is formulated in the
classical way: the given set of probabilities on phase space is viable if and
only if the set of tangent distributions intersects with the set of
distributions feasible by virtue of dynamics.
