A book of business is the set of client relationships an adviser serves, together with the revenue those relationships generate. Whether the adviser owns it or the firm does is the defining question of the independence decision.
Inside a wirehouse, the clients are generally the firm's. In an independent RIA, they are the firm's, and the adviser owns the firm.
That distinction determines whether decades of work produces a sellable asset or a salary.
Usually as a multiple of recurring revenue, adjusted for what actually drives durability: client age distribution, revenue concentration in a few relationships, growth rate, and how dependent the relationships are on one person.
A book where every client relationship runs through the founder is worth less than one with the same revenue and a team, because the buyer is acquiring something that may not survive the founder's departure.
That is uncomfortable, because the same personal service that built the book is what discounts it.
What an adviser may say to clients when leaving is governed by their agreements and by law, not by fairness. It is a question for a lawyer with the actual documents.
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