With economic output of about $17 billion, the Estonian economy is tiny. Yet the country’s central bank governor, Andres Lipstok, will now be able to take a seat on the European Central Bank’s powerful council that sets interest rates.

Membership is also an important signpost that a country is on the way to achieving Western European standards of living, an important goal for a former Soviet republic like Estonia that has long been among the Baltic states eager to develop.

Perhaps most important, membership is recognition of the hard work and sacrifice it took to keep Estonia’s bid on track. Estonia, along with Sweden, were the two countries with the smallest shortfalls between revenue and spending among all members of the 27-member European Union. Moreover, public debt in Estonia at 7.2 percent of gross domestic product is tiny compared with that of most other countries in the bloc.

“It’s a great day for Estonia,” Andrus Ansip, the Estonian prime minister, told Latvian state radio in an interview here. “We prefer to be inside, to join the club, to be among decision makers.”

Estonia becomes the third ex-Communist state to make the switch to the euro, after Slovenia and Slovakia, but it is the first former Soviet republic to do so, sending a signal to other countries in Central and Eastern Europe that they, too, can aspire to membership.

That said, the euro zone is not expected to expand further for some time to come as other candidates like the Czech Republic, Hungary, Latvia, Lithuania, Bulgaria, Romania and Poland still fall short of the entry criteria partly because of their large budget deficits.

Image Estonians at a cafe in Tallinn, the capital, last month. A menu displays prices in the kroon and the euro. Estonia will begin using the euro on Jan. 1. Credit... Ints Kalnins/Reuters

And the accession of Estonia will do little to erase the chief criticism of the euro project: that Europe’s nations are too economically disparate to maintain supranational institutions like a single currency in the long term.