Since 1996, Ukraine’s executive-legislative relations have been characterized by a semi-presidential system with several subperiods: president-parliamentarism (1996–2006, 2010–2014) and premier-presidentialism (2006–2010, 2014–present). This chapter provides an overview of the factors that led to the adoption of semi-presidentialism in Ukraine and the effects that its two subtypes have had on Ukrainian politics, particularly in the relationship between the president, the government, and parliament. We analyze how these two subtypes of semi-presidentialism impacted democratic development and shifted the balance of power within a subtype without constitutional changes. Additionally, the chapter describes how informal politics, particularly patronal politics and clientelism, have influenced the functioning of formal institutions in Ukraine and how these informal structures have persisted beyond systemic crises in 2004 and 2014. The final section focuses on the internal development and institutionalization of the Ukrainian parliament, examining five indicators: (1) the parliamentary party system, (2) the partyness of parliament, (3) the nature of parliamentary majorities, (4) parliamentary influence in legislative production, and (5) permanent specialized committees.