Ukraine’s foreign policy has puzzled observers since the dissolution of the Soviet Union due to its unusual inconsistency. This inconsistency exhibited itself in contradictory decisions by the Ukrainian executive carried out within a short period of time, which signalled either greater cooperation with Russia and relative cooling of relations with the West, or integration into Western institutions and worsening of the relations with Moscow. This study aims to explain the inconsistency by examining the sources of Ukraine’s foreign policy through process-tracing in four policy cases: Ukraine’s renouncement of nuclear weapons (1991-1994), the status of the Black Sea Fleet (1991-1997), the Odesa-Brody pipeline (2002-2004), and the 2006-2009 gas disputes. Contrary to dominant interpretations of Ukraine’s foreign policy vacillation that emphasise the role of external influences, especially that of Russia and the West, this study concludes that Ukraine’s inconsistent foreign policy decisions are best explained by domestic factors – intra-executive divisions and the influence of vested interests on policy-making. The work relies on the use of primary sources including archival research, elite interviews, and Ukrainian and Russian newspaper reports.