The upheaval in 2014 led to Russia annexing the Crimean Peninsula from Ukraine in a move that Ukraine and most of the world views as illegal. It also led to a separatist conflict in eastern Ukraine that has killed more than 13,000 people and to economic decline.
A look at some of the issues at stake as Ukraine chooses a new president: CORRUPTION Endemic corruption was one of the key complaints against the president ousted in 2014 and persists under his successor, Petro Poroshenko. Transparency International's Corruption Perceptions Index shows Ukraine at 120 among 188 countries rated for clean government -- a marginal improvement from recent years but still in the neighborhood of notably dodgy countries such as Niger and Mali.
Poroshenko initiated some anti-corruption measures that were demanded by the International Monetary Fund for the release of billions of dollars in loans. But the fledgling efforts suffered a considerable blow this month when the main anti-corruption law was declared unconstitutional. State defense enterprises, meanwhile, are embroiled in a military embezzlement scandal.
Top candidates have vowed various severe measures against corruption, including mandatory life in prison for cheating the military, lifetime bans on holding public office and a onetime tax amnesty for hidden assets. But corruption is so pervasive that such measures could show little effect, while rising public anger demands more visible action.
All the top candidates pledge they will pursue European Union membership for Ukraine, but the bloc appears reluctant to welcome a country that can't or won't tackle corruption. RUSSIA The top candidates also favor Ukraine seeking NATO membership, a move that would be anathema to Russia and that could obstruct attempts to resolve other tensions such as the war in eastern Ukraine and Russia's seizure of 24 Ukrainian sailors last year.
The prospects of any resolution of the conflict in the east are dim, though the top candidates have different approaches of how to tackle the issue. Poroshenko, who is seeking a second term, favors the so-called Normandy Format talks of Russia, Ukraine, France and Germany, although those negotiations have been all but dormant. Yulia Tymoshenko wants talks held among the signatories of the Budapest Memorandum, which calls observing the territorial integrity of former Soviet republics that gave up their nuclear weapons, even though Russia flouted that pact when it annexed Crimea.
Upstart Volodymyr Zelenskiy says the matter can be solved only through direct talks with Russia. That idea has received some favorable news coverage in Russia, suggesting Moscow is looking for a way out of a conflict that has cost it heavily in international sanctions.
QUALITY OF LIFE Daily life for many Ukrainians is poor and dismal — the average wage is just $350 a month. Thus, a 25-percent hike in prices for natural gas last year was a severe blow to many households.
Tymoshenko likened that to "genocide" and has vowed to cut gas prices by 50 percent or more. But doing so would risk the disapproval of the international financial institutions giving Ukraine aid; the price hike met demands for the gas market to be rationalized.
Ukraine's medical care system, largely unchanged since the Soviet era, has been notoriously poor, especially outside major cities. Reforms are underway, but some candidates say the changes are insufficient and make access to general practitioners difficult. Tymoshenko and Zelenskiy both propose introducing medical insurance.
ECONOMY Ukraine's economy is recovering from the severe decline it experienced after the 2014 upheaval, but gross domestic product is still substantially below its level in 2013. The willingness of the next president to undertake reforms — and the composition of the new parliament to be elected in September — will likely promote or discourage investors. Before the presidential vote, economists were predicting modest growth of about 2.5 percent a year, marred by inflation expected at about 10 percent.
Poroshenko can point to the economic improvement during his tenure, including a rise in foreign direct investment. Zelenskiy calls for simplifying the tax code and for removing obstructions to new enterprises, so that "you can open a business in an hour." Tymoshenko has promised to lower the tax on entrepreneurs by half and to redirect Ukraine's economy from reliance on raw materials to producing finished goods.
DEMOCRACY Regardless of who wins, the election will be a significant test of Ukraine's commitment to orderly democracy, influencing both citizens' trust in the authorities and international partners. The pre-election period has been increasingly messy. Poroshenko's own interior minister has accused the president of using public money to try to buy votes.
After Zelenskiy's campaign found listening devices in its Kiev building, an Interior Ministry official suggested the national security service was involved and the security service in turn opened a criminal case against the ministry on the grounds of undermining state security.
Far-right groups have become increasingly unruly as the campaign period progressed.