This paper uncovers novel facts about serial entrepreneurship at the top of the wealth distribution. While business ownership is prevalent among the richest households, top business wealth is not simply built by scaling a single large firm. In the SCF, business-owning households in the top 0.1 percent own about seven private businesses on average, while Forbes-listed individuals own around ten. These portfolios are active and dynamic. Entrepreneurs enter new ventures, scale some of them, close or sell others, and reallocate capital across them. Private equity returns fall sharply with wealth for single-firm owners, but much less for entrepreneurs with multiple firms. We develop a tractable general equilibrium theory in which entrepreneurs operate multiple firms subject to decreasing returns and search for high-yield opportunities. The model matches the concentration of multi-firm entrepreneurs at the top, the flows into and out of multi-firm ownership, and the flatter returnwealth profile among rich households. Wealth taxation has ambiguous effects. It improves selection toward high-return entrepreneurs, but weakens experimentation at the top.