Investment treaties grant foreign investors certain protections, which they can invoke before international arbitral tribunals. Those treaties do not apply to local investors. This different treatment raises constitutional objections based on the principle of equality. Courts in various jurisdictions have had to deal with this challenge when ruling on the constitutionality of investment treaties. The different treatment that derives from the current investment regime is sometimes defended on the instrumental ground that it helps attract external capital, which is beneficial for the economy of the host state. Another theory, in contrast, argues that investment treaties are necessary to counteract the potential vulnerability of foreigners. The chapter develops an equality-based theory that constitutional courts could use in their decisions, and explores the doctrinal legal consequences that should follow from it.