Because of the damaging winds and other severe weather threats with which they are associated, derecho-producing MCSs pose an important challenge to forecasters. During the late spring and summer, derechos typically occur in environments of substantial convective instability, with very moist boundary layer inflow. During the cool season, these events are more commonly associated with amplifying disturbances in the westerlies. While cool season derechos sometimes occur with only a modest degree of convective instability, the boundary layer inflow associated with most such events is relatively moist for the season. Occasionally, however, long-lived, cool-season derecho-producing MCSs occur with very dry boundary layer conditions (surface dewpoints at or below 10 C). Low dewpoint derechos have also been observed in summer. Because low dewpoint derechos develop in environments not commonly associated with widespread damaging thunderstorms, these events sometimes catch forecasters by surprise. This paper will examine several low dew point derecho cases that have occurred in recent years, with emphasis on the synoptic and mesoscale factors that appear to have been important to their development.