• The Lean StartupEric Ries, 2011The three engines of growth, sticky, viral and paid, and the advice to tune one at a time.
• "Growth Loops are the New Funnels"Brian Balfour, Casey Winters, Kevin Kwok, Andrew Chen, Reforge, 2018The case for drawing growth as loops, where each cycle's output becomes the next cycle's input.
• "Lessons Learned: Viral Marketing"David Skok, For EntrepreneursThe viral growth formula with cycle time, used in Loop Math.
• The Cold Start ProblemAndrew Chen, 2021Atomic networks, the hard side, and how networks tip, scale and stall.
• Hacking GrowthSean Ellis and Morgan Brown, 2017How growth teams find the moment a product clicks and test quickly around it; Ellis worked with Dropbox early.
• Viral LoopAdam L. Penenberg, 2009Early histories of companies that grew through their users, including PayPal and eBay.
• HookedNir Eyal, 2014Trigger, action, variable reward, investment: the habit loop inside a customer that feeds the loop between customers.
• Thinking in SystemsDonella Meadows, 2008Reinforcing and balancing loops, stocks, flows and delays.
• The Fifth DisciplinePeter Senge, 1990Limits to growth and the other patterns that stall a loop.
• Turning the FlywheelJim Collins, 2019How to write your own flywheel, and why the order of its parts matters.
• InfluenceRobert Cialdini, 1984Reciprocity, social proof and scarcity: the psychology inside every double-sided reward and giveaway.
• ContagiousJonah Berger, 2013Why some things get talked about, and how to design for it.
• Zero to OnePeter Thiel with Blake Masters, 2014Distribution as part of the product, from someone who ran PayPal's loop.
• BlitzscalingReid Hoffman and Chris Yeh, 2018Growth when speed matters most, with PayPal and eBay from the inside.
• The ContrarianMax Chafkin, 2021The source used here for PayPal's early bonus amounts and user counts.
• The PayPal WarsEric M. Jackson, 2004An insider's history of PayPal's fight with eBay and fraud.

What most of these books leave out is what this one tried to add: loops that ship physical goods with margins, rewards that fall under sweepstakes and consumer law, and proof from a holdout rather than a dashboard.