  We develop a theory of monotone comparative statics for models with
adjustment costs. We show that comparative-statics conclusions may be drawn
under the usual ordinal complementarity assumptions on the objective function,
assuming very little about costs: only a mild monotonicity condition is
required. We use this insight to prove a general le Chatelier principle: under
the ordinal complementarity assumptions, if short-run adjustment is subject to
a monotone cost, then the long-run response to a shock is greater than the
short-run response. We extend these results to a fully dynamic model of
adjustment over time: the le Chatelier principle remains valid, and under
slightly stronger assumptions, optimal adjustment follows a monotone path. We
apply our results to models of saving, production, pricing, labor supply and
investment.
