The article focuses on cross-border cooperation of post-Soviet de facto states (Abkhazia, Donetsk, and Lugansk people’s republics, Pridnestrovian Moldavian Republic, and South Ossetia) from the early 1990s until 2021. The author argues that in the most of examined cases cross-border cooperation of post-Soviet de facto states is not particularly effective. It can be largely explained by de facto states’ complicated political relations with some adjacent recognized states, the illegitimacy of de facto borders for many potential partners, limited economic potentials of de facto states, perceiving them as a potential source of threats and instability even by friendly adjacent legitimate states, and over-centralized management of cross-border interactions by governments. Despite numerous problems, cross-border cooperation between post-Soviet de facto states and adjacent provinces of the relevant patron state (that is Russia) largely contributes to solving a de facto state’s survival problems in the domains of health care, communication, and economic development. It should be noted that Russia’s cooperation with those de facto states whose independence it has recognized is much more dynamic than cooperation with a non-recognized state. Cross-border cooperation between parent states and their “breakaway territories” is in its infancy in most cases. Relatively successful cooperation between Moldova and Transnistria can be considered as a partial exception but even in this case cooperation is periodically complicated with political contradictions. Finally, cross-border cooperation of a de facto state with a third country (Ukraine-Transnistria) is complicated with non-recognition and unfavorable political situation, while cooperation between two de facto states (between Donetsk and Lugansk People’s Republics) by hypercentralized governance in both republics.