Bilateral investment treaties (BITs) are legal instruments used by developing and transition countries to provide investor protection and, by extension, promote higher levels of inward foreign direct investment (FDI). While the link between BITs and FDI has been extensively studied, little is known about the impact of the treaties on different forms of investment. Motivated by this observation, we examine the effects of BITs on vertical and horizontal FDI. We find that BITs are more positively related to vertical than to horizontal FDI. We also find that BITs tend to act as stronger substitutes for better institutions in the case of vertical relative to horizontal investments. The findings inform BIT strategies that are compatible with development objectives in developing and transition countries.