Book of business (definition)
The portfolio of client accounts and their renewable revenue; the asset an agency actually owns and sells.
A book of business is the portfolio of client accounts, policies, and renewable commission revenue attached to an agency or a producer. It is the asset the business actually owns; offices and systems are furniture by comparison.
Books are described by their composition: personal versus commercial, line mix, carrier mix, account size, and geography. Two books with identical revenue can be very different assets depending on retention, concentration, and who controls the relationships.
In M&A, the book is what transfers. Diligence tests its durability: retention history, account concentration, producer dependence, and the quality of the expirations data behind it.