The UN has begun consultations with Syrian government and opposition officials as it seeks to find enough common ground to restart peace talks.
Special envoy Staffan de Mistura said more than 40 groups had been invited to attend one-on-one meetings over the next five to six weeks.
Iran and Turkey have also been invited, but jihadist militant groups have not.
Mr de Mistura described it as a stock-taking process, saying there would be no big roundtable discussions.
The last round of peace talks in Geneva collapsed in early 2014 with the government refusing to discuss opposition demands.
'No cut-off date'
The talks in Geneva are being billed by the UN as low-key consultations rather than real negotiations, reports the BBC's Imogen Foulkes in the Swiss city.
The goal is to find areas where negotiation, even on a modest temporary ceasefire in some towns, might be possible, she says.
"These are not yet peace talks," Mr de Mistura stressed at a news conference, acknowledging that the chances of success were slim.
None of the different groups will meet one another. Instead, representatives of "a broad spectrum of youth, political and military actors, women, victims, civil society, diaspora, religious and community leaders", as well as 20 countries, will have individual meetings with the special envoy.
Mr de Mistura said there was "no cut-off date" and that at the end of June he would "assess progress" and "decide on the next steps".
The Swedish-Italian diplomat said he wanted to identify possible negotiating positions and try to "operationalise" the 2012 Geneva Communique, an internationally-backed agreement that called for the establishment of a transitional governing body in Syria formed on the basis of mutual consent.
Although the UN is seeking a political solution based on the communique, Mr de Mistura noted that it had neither become reality nor had there been a serious discussion on how to implement it.
Even before the consultations began on Tuesday, doubts were being expressed, our correspondent says.
Some opposition groups were angry that Iran - President Bashar al-Assad's staunch ally - had been invited, claiming it showed Mr de Mistura was too close to the Syrian government.
Jihadist groups like Islamic State and al-Nusra Front, al-Qaeda's affiliate in Syria, will also not be there as they are designated as terrorist organisations by the UN.
But some diplomats point out that given the power these two groups have on the ground in Syria, any peace deal would have to involve them somehow, our correspondent adds.