We are delighted to present this special issue of The Knowledge Engineering Review, as it marks a significant accomplishment of the case-based reasoning (CBR) community. Its 19 commentaries, written by 41 authors, represent a compendium on the state-of-the-art in CBR. These evolved from a 2003 workshop that was held at Waiheke Island and Queenstown, New Zealand and chaired by Alec Holt and Ian Watson. The workshop's delegates identified the primary topics of CBR research and application, selected representative influential publications for each topic, and were encouraged to co-author commentaries on each topic with other CBR experts who were unable to attend. These collaborations produced the articles you now see. While several reviews exist on CBR (e.g. Marir & Watson, 1994; López de Mántaras & Plaza, 1997; Lenz et al., 1998), few have been published recently or have similar historical and subject breadth.