Kathleen Thelen is one of the leading scholars studying incremental institutional change. In her early works from the 1990s, she introduced the conceptualization of different modes of incremental change. These modes have central attention in her recent co-edited book with James Mahoney, Explaining Institutional Change (2010). Compared with Thelen's earlier work, this book provides clearer definitions, addresses the explanatory factors of institutional change, and discusses the patterns and sequences of gradual institutional change. The theory presented by Mahoney and Thelen, however, seems overambitious and subject to a need to be overly crisp and clear.