Only two parties in Poland can be sure of winning substantial numbers of parliament seats in Sunday's general elections: the ruling Civic Platform party and the largest opposition party, Law and Justice, the leader in opinion polls. One or more small parties could end up as coalition partners of the winner.

Here is a look at the two main parties:

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CIVIC PLATFORM: the leading force in a coalition government with the small Polish People's Party, in power since 2007.

Prime Minister Ewa Kopacz took over as government and party leader in 2014 from Donald Tusk, now president of the European Union.

Tax policy: tax exemptions for those earning the least and for employers to encourage new jobs. Tax exemptions for families with children.

Euro: in favor of adopting the euro one day, but no date set.

Climate: supports coal as a main source of energy and jobs. Poland repeatedly vetoed EU climate policy but eventually joined in.

Jobs: temporary job agreements without health care or pension rights proliferated under the party's rule; it now vows to limit them.

Social issues: Civic Platform raised the retirement age to 67 from 60 for women and 65 for men to help the strapped pensions fund. It implemented state funding for in vitro fertilization. It supports civic partnerships for gay and straight couples, but has not campaigned strongly for that.

Migrants: no to economic migrants, but the government has agreed to take 7,000 refugees from Syria and Eritrea as part of an EU plan.

Religion: wants to end state funding of religious denominations.

EU and national security: wants Poland to have a strong position in the EU and a greater U.S. and NATO military presence in the country.

Electorate: support is strongest in big cities, among secular Poles and among those who have benefited from the transition to a market economy following communism's collapse 26 years ago.

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LAW AND JUSTICE: largest opposition party, mixes Catholic values with welfare policies. It was in power from 2005-2007.

Tax policy: wants new taxes on foreign-owned banks and supermarket chains; tightening the tax collecting system, especially for VAT and corporate tax; lowering the personal income tax, and cash allowances to poorest families with children.

Euro currency: Poland's currency, the zloty, should be preserved.

Climate: Wants to renegotiate EU climate policy agreement which it says blocks the nation's development.

Jobs: some 1.2 million new jobs promised and higher pay for young people to stop them from emigrating.

Social issues: reversal of Civic Platform's increase of the retirement age. Party opposes IVF, abortion, gay marriage.

Migrants: migrants and refugees should not be accepted; financial aid should be offered to refugees in Middle East camps.

Religion: Catholic Church should preserve its role as a moral authority and be supported by the state.

EU and national security: EU should respect Poland's interests. More NATO and U.S. troops needed in Poland.

Electorate: support is very strong in the countryside, among older Poles and those who struggle on low wages or who have otherwise not prospered in the capitalist era.

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There are several small radical right-wing parties and a coalition of left-wing parties. A new small left-wing party, razem (together), became a sensation after doing well in a televised debate on Tuesday.

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VOTING SYSTEM: In voting between 7 a.m. and 9 p.m. local time (0600GMT to 2000GMT) Poles will choose 460 lawmakers and 100 senators for terms of four years. The State Electoral Commission says 30.7 million people are eligible to vote in the nation of 37.4 million.

Voters can mark only one candidate from one party, and that counts as a vote for the party and for the candidate. Eight parties are competing nationwide and another seven compete in fewer constituencies.

The party that gets the most votes nationwide is the winner and gets a proportionate number of seats in parliament. Its lawmakers are those who received the highest number of votes on the party list.

A party needs to win at least 5 percent of valid votes and a coalition at least 8 percent of valid votes to enter parliament.