A simple model is presented in which it is costly for domestic investors to hold foreign assets. The implications of the model for the composition of optimal portfolios at home and abroad are derived. It is shown that all foreign assets with a beta larger than some beta β * plot on either one of two security market lines. Some foreign assets with a beta smaller than β * are not held by domestic investors even if their expected return is increased slightly.

A simple model is presented in which it is costly for domestic investors to hold foreign assets. The implications of the model for the composition of optimal portfolios at home and abroad are derived. It is shown that all foreign assets with a beta larger than some beta plot on either one of two security market lines. Some foreign assets with a beta smaller than are not held by domestic investors even if their expected return is increased slightly.

In this paper, the authors show that Tobin's q and firm diversification are negatively related throughout the 1980s. This negative relation holds for different diversification measures and when they control for other known determinants of q. Further, diversified firms have lower q's than comparable portfolios of pure-play firms. Firms that choose to diversify are poor performers relative to firms that do not but there is only weak evidence that they have lower q's than the average firm in their industry. The authors find no evidence supportive of the view that diversification provides firms with a valuable intangible asset.