Of the nine new countries, eight are ex-communist states, and three of those were Soviet republics. The event has widely been hailed as the final disappearance of the Iron Curtain.
Former Warsaw Pact members the Czech Republic, Hungary, Poland, Slovakia, and the three ex-Soviet Baltic States Estonia, Latvia, and Lithuania, along with Slovenia, all held their own ceremonies at border towns at midnight. Maltese government ministers are set to mark the event with a sea voyage to the Italian island of Sicily.
Four of the countries - Poland and the three Baltic nations - share borders with Russia.
At the Austrian town of Berg on the once heavily-fortified Slovak border, Austrian Chancellor Alfred Gusenbauer and Slovak Prime Minister Robert Fico sawed through a barrier in front of a cheering crowd, an image that was broadcast across Europe.
German Chancellor Angela Merkel, Polish Prime Minister Donald Tusk, and Czech premier Mirek Topolanek will hold a ceremony on Friday morning in the southeast German town of Zittau, near the borders with Poland and the Czech Republic. European Commission President Jose Manuel Barroso will attend the event.
The Schengen zone now covers much of the European Union, as well as non-EU members Norway and Iceland. The United Kingdom and Ireland have opted out of the agreement, and new EU members Romania and Bulgaria have yet to meet security requirements to join the zone. Cyprus and possibly Switzerland will open their borders to Schengen members next year.
The newly-expanded region for passport-free travel stretches over 24 countries, home to a total of 400 million people, more than the population of the United States.
The freeing of borders applies to land and sea only, but as of March 2008 will be extended to airports.
The lifting of internal controls will free up tourist travel within the zone, in particular for foreigners entering the European Union. Ethnic Russians living in Estonia and Latvia, many of whom have been denied citizenship and have "non-resident" status, will now be able to travel throughout much of Europe without having their identity cards and residence permits inspected. Until January 2007, "non-residents" had required visas to enter other EU states.
The Russian Tourism Union's press secretary, Irina Tyurina, said Schengen's expansion will make life easier for Russian tourists, allowing them "to visit 24 countries all at once with just one visa."
However, she said the inflow of Russian tourists into the European Union would not alter, despite simplified visa procedures.
The new member states "have already been working according to Schengen rules for a long time, so in reality nothing will change for tourists... The number of people that travelled - that number will still travel," she said.
Konstantin Kosachyov, who heads the International Affairs Committee of the lower house of Russia's parliament, warned that the expanded zone could result in higher visa costs for residents of the Kaliningrad Region, Russia's Baltic exclave bordering on Lithuania and Poland.
The changes "will make life easier for Russian citizens, with one exception, for which a solution has yet to be found. This exception is the Kaliningrad Region," Kosachyov told RIA Novosti.
The region until now had special arrangements with its EU neighbors, allowing its residents to cross those countries' borders with visas that could be acquired either very cheaply or free of charge. Obtaining Schengen visas could now prove more expensive for residents, he said.
"Russia's Foreign Ministry is currently in consultations with the European Union, in particular Poland and Lithuania, on this issue," Kosachyov said.
The Schengen agreement is named after the Luxembourg village where it was signed by the first members in 1985. The zone initially encompassed Belgium, the Netherlands, Luxembourg, France, and Germany.