The research covers the early years of Ukraine’s and Poland’s cooperation in their bilateral relations in the context of building up security policies between the NATO and the CSTO in 1991–1994. Various information influences from state and non-state actors, internal and external, made it so the processes of the search for security guarantees ended up quite different between the two neighboring countries. Covering sources and literature that provide evidence for influences from sources such as the Kremlin, the non-lustrated “old guard” former Communist party functionaries in Ukraine, and the former opposition in Poland, the research shows how the two countries’ relations with the NATO differed, and why, though both countries joined the Partnership for Peace program at roughly the same time, Poland managed to start active Euro-Atlantic integration much earlier than Ukraine did. Using sources such as the text of the treaties, the establishing documents and legislature guidebooks of organization, public writings of diplomats and former policy makers, the research shows what exactly were the risks that the NATO assessed in the joining of former Eastern Bloc countries (with the unstated reasons for the small number of contacts of those countries with NATO in the 1991–1994 relevant to the West’s suspicion of post-Soviet intelligence and military), and which points of the first Ukraine-NATO proved “too much” for the former. Furthermore, Ukraine’s early success with the number of NATO exercises it partook in during the first years of the Partnership for Peace became an example to other Eastern Europe countries seeking better relations with NATO and defense sector reforms, including the Republic of Poland. The paper also highlights the tendencies of cooperation between Ukraine and the Republic of Poland in the context of NATO enlargement and the various aspects of Atlantic integration. The most important among them was cooperation in security and defense, both bilateral and within the framework of the NATO Partnership for Peace Program.