I examine the time‐series variation in corporate credit rating standards from 1985 to 2007. A divergent pattern exists between investment‐grade and speculative‐grade rating standards from 1985 to 2002 as investment‐grade standards tighten and speculative‐grade loosen. In 2002, a structural shift occurs towards more stringent ratings. Holding characteristics constant, firms experience a drop of 1.5 notches in ratings due to tightened standards from 2002 to 2007. Credit spread tests suggest that the variation in standards is not completely due to changes in the economic climate. Rating standards affect credit spreads. Loose ratings are associated with higher default rates. This article is protected by copyright. All rights reserved.