This article focuses primarily on theory because its subject, international investment law (hereinafter - «IIL»), is a relatively new and developing phenomenon within the system of international law (hereinafter - «IL»).

The author made an attempt to determine the place of IIL within the system of IL and to understand whether IIL is an independent branch of IL or just a sub-branch/institute within the frame of already existing (recognized) branches of IL.

For this purpose the article contains analysis of the main works of foreign and Russian authors on this topic. Different opinions regarding the place of IIL within the system of IL are researched and compared in the article.

On the basis of comprehensive analysis the author emphasizes the dominating and the most reasonable, in his point of view, opinion referring IIL to a sub-branch of international economic law.

At the same time the author agrees that there is no common view as to the place of IIL within the system of IL. This fact supports the conclusion arrived to by the author that currently IIL is at the stage of active development.