Recent empirical studies have indicated that spin-offs are value enhancing, yet the theoretical aspects of spin-off gains have not been as well explored. This paper presents a theoretical analysis of spin-offs. In the model of the firm presented, outstanding risky debt gives rise to agency costs of underinvestment, which are offset by the benefit of debt-related tax shields. The trade-off specifies the optimal leverage for a firm. Within this framework, the paper considers whether and under what circumstances firm value could be enhanced by a spin-off. It is shown that a spin-off in which parent company debt is optimally allocated between the post-spin-off firms increases value by reducing agency costs and increasing the value of tax shields when the component firm cash flows are positively correlated. The optimal allocation is characterized in terms of the parameters of the technologies of the component firms. When the component cash flows are negatively correlated, under the sufficient conditions developed, a combined firm operation dominates spin-offs. Here, the coinsurance effect on investment incentives dominates the effect of a flexible allocation of debt across technologies in a spin-off.