• Profit from the CoreChris Zook with James Allen, 2001The argument that growth starts with a strong core. Read it for the frame, and read its numbers as a consultancy’s reported data.
• Beyond the CoreChris Zook, 2004The six kinds of adjacency and the idea of counting steps from the core. The most useful of the trilogy for choosing a next category.
• The Wallet Allocation RuleTimothy Keiningham, Lerzan Aksoy, Luke Williams and Alexander Buoye, 2015Why rank beats satisfaction for predicting share of wallet, and how to measure it. The basis of chapter 2.
• Co-opetitionAdam Brandenburger and Barry Nalebuff, 1996The value net and complementors. Read it before you build anything a partner already makes.
• The Halo EffectPhil Rosenzweig, 2007Why studies of successful companies mislead, and how to read one. The antidote to every “what the winners did” book, including the first two on this shelf.
• King of CapitalAmey Stone and Mike Brewster, 2002Sandy Weill and the building of Citigroup: the cross-selling thesis told from inside, before it was unwound.

And the research: Peng and colleagues’ 2023 meta-analysis on brand extensions, Reinartz, Thomas and Bascoul (2008) and Shah, Kumar, Qu and Chen (2012) on cross-buying, and Sharma, Hofman and Watts (2015) on what recommendations cause. Full references are in Appendix C.