Andrew Rosenblum founded Bonsai Partners in 2018 after gaining experience as an investment professional at Matrix Capital Management (2011-2016) and serving as Manager of Strategic Planning at Adaptive Biotechnologies (2016-2017). He holds a degree from the Ross School of Business at the University of Michigan and passed the Series 65 examination in May 2018. Rosenblum prefers maintaining a concentrated portfolio allowing for deep investigative research that he describes as an artistic pursuit rather than purely scientific analysis. He emphasizes finding companies where both great business quality and great pricing converge to earn spectacular results. In 2025, the firm added Nico Kirsten as CFO, bringing over twenty years of fund accounting and finance experience from firms like StepStone Group and PwC. Both leaders reside in San Diego, reflecting the firm's California-based operations and culture.

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Bonsai Partners was created out of a belief that active management, when approached with deliberate thought and care, can put investors in the best position to succeed. The firm employs a unique investment framework called 'Enduring Economics,' combining competitive advantage with customer advantage through 'radical customer alignment.' Their mandate is deliberately broad, placing no limits on sectors, geographies, or company sizes, instead focusing on whether they understand the business, trust its leaders, align with company objectives and values, and find acceptable pricing. The fund maintains a concentrated portfolio of 5-15 high-conviction unusual public equity investments, emphasizing business robustness through diversification across value chains or outright ownership of key processes. They avoid fragile businesses that cannot withstand unforeseen risks, preferring companies that demonstrate adaptability and long-term durability. The investment approach has evolved toward long-term investing with greater portfolio stability and fewer changes year-over-year.

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