  Mill's classic argument for liberty requires that people's exercise of
freedom should be governed by a no-harm principle (NHP). In this paper, we
develop the concept of a no-harm equilibrium in $n$-person games where players
maximize utility subject to the constraint of the NHP. Our main result is in
the spirit of the fundamental theorems of welfare economics. We show that for
every initial `reference point' in a game the associated no-harm equilibrium is
Pareto efficient and, conversely, every Pareto efficient point can be supported
as a no-harm equilibrium for some initial reference point.
