President Tayyip Erdogan is aiming to extend his 20-year rule in elections that will decide not just who leads Turkey but how it is governed, where its economy is headed and what role it may play to ease conflict in Ukraine and the Middle East.
The presidential and parliamentary elections, which must be held by June, mark the biggest political challenge yet for Erdogan, who has championed religious piety, military-backed diplomacy, and low interest rates.
Should he lose, his opponents promise radical change.
WHAT'S AT STAKE IN THIS ELECTION FOR TURKEY...
The most powerful leader since Mustafa Kemal Ataturk founded the modern Turkish republic a century ago, Erdogan and his Islamist-based AK Party have shifted Turkey away from Ataturk's secular blueprint.
Erdogan has also centralised power around an executive presidency, based in a 1,000-room palace on the edge of Ankara, which sets policy on Turkey's economic, security, domestic and international affairs.
Critics say his government has muzzled dissent, eroded rights and brought the judicial system under its sway - a charge denied by officials who say it has protected citizens in the face of unique security threats including a 2016 coup attempt.
Economists say his calls for low interest rates set inflation soaring to a 24-year high of 85% last year, and the lira slumping to one tenth of its value against the dollar over the last decade.
Opposition parties have pledged to restore central bank independence, bring back parliamentary government and introduce a new constitution enshrining the rule of law.
...AND THE REST OF THE WORLD?
Under Erdogan, Turkey has flexed military power in the Middle East and beyond - launching four incursions into Syria, waging an offensive against Kurdish militants inside Iraq and sending military support to Libya and Azerbaijan.
Turkey also saw a series of diplomatic clashes with regional powers Saudi Arabia, the United Arab Emirates and Israel, as well as a standoff with Greece and Cyprus over eastern Mediterranean maritime boundaries, until it changed tack two years ago and sought rapprochement with some of its rivals.
Erdogan's purchase of Russian air defences triggered US arms industry sanctions against Ankara, while his closeness to President Vladimir Putin led critics to question Turkey's commitment to the NATO Western defence alliance. Ankara's objections to NATO membership applications from Sweden and Finland have also raised tensions.
However, Turkey also brokered a deal for Ukrainian wheat exports, underlining the potential role Erdogan has staked in efforts to end the Ukraine war. It is not clear that a successor would enjoy the same profile he has created on the world stage - a point he is likely to stress in the election campaign.
COULD THE ECONOMY BRING ERDOGAN DOWN?
While the first of Erdogan's two decades in power was marked by surging economic growth, the last 10 years have seen a decline in prosperity which has hit his popularity with voters.
His AK Party is still the strongest party and likely remain a powerful force in parliament, but opinion polls show Erdogan trailing against some potential opposition presidential candidates.
Knowing that the rising cost of living threatens his re-election prospects, Erdogan has announced a doubling of the minimum wage in a package of measures which will also allow more than 2 million workers to retire early.
WHAT ARE THE OPPOSITION PROMISING?
The two main opposition parties, the secularist Republican People's Party (CHP) and centre-right nationalist IYI Party, have allied themselves with four smaller parties under a platform that would reverse many of Erdogan's signature policies.
They have pledged to restore independence to the central bank and reverse Erdogan's unorthodox economic policies. They would also dismantle his executive presidency in favour of the previous parliamentary system, and send back Syrian refugees.
Erdogan supported failed efforts to topple President Bashar al-Assad, while hosting more than 3.6 million Syrian refugees who have become increasingly unwelcome amid economic hardship in Turkey.
He has recently echoed opposition calls for rapprochement with Damascus and talked about returning some refugees, although neither the president nor opposition has set out how that could safely take place.
WHAT'S STOPPING THE OPPOSITION?
The six-party alliance is seeking to forge a united platform but has yet to agree a candidate to challenge Erdogan for the presidency.
CHP leader Kemal Kilicdaroglu is seen as a lacklustre campaigner. Another contender, the CHP mayor of Istanbul, was handed a jail sentence and political ban in December for insulting election officials - a conviction he is challenging.
Meanwhile Turkey's top court is hearing a case to shut down the third-largest parliamentary party, the pro-Kurdish Peoples' Democratic Party (HDP), and has frozen some of its accounts. The HDP former leader Selahattin Demirtas has been in jail since 2016 on charges of insulting the president.
Once campaigning starts, opposition parties may find it harder to get their message heard. In the 2018 presidential election they struggled for air time on Turkish television channels which are mostly strongly supportive of Erdogan.
WHAT HAPPENS NEXT?
Though the election deadline is mid-June, Erdogan's party has said they may be brought forward.
The opposition alliance's choice of candidate could be key to their chances of victory, but other factors will be in play including prospects for reining in inflation.
Erdogan has floated the possibility of a summit with Syria's Assad, a possible first step in discussions about the future of refugees. At the same time, Ankara has warned for months that it is preparing for a fresh offensive in northern Syria targeting Kurdish fighters - which could boost Erdogan's ratings.