Although the signing ceremony is a giant step for Nabucco, critics point out that still left unresolved is the problematic question of Turkey's demand that 15 percent of the gas that will go through the pipeline be given to it for its domestic use or for re-export. The European Union has said the Turkish demand is unacceptable. Monday's ceremony, though, may be a sign that both sides foresee a resolution to that issue.
I'll have more about this next week. For now, take a look at this useful Q&A Reuters has put together about Monday's signing ceremony and what it means.