Leaders of several European parties on the far right have gathered in the Polish capital to discuss issues such as sovereignty and migration.
The association will be the European Parliament's second largest political group.
But the goal of creating a formal alliance in the European Parliament did not succeed.
Participants in the Warsaw summit included Hungarian Prime Minister Viktor Orbán, French opposition politician Marine Le Pen and host Jaroslaw Kaczynski of the ruling Law and Justice party.
- It is a very welcome step forward and it makes me very optimistic about the future, Marine Le Pen said after the meeting, according to the news agency AP.
The party leaders also agreed to hold meetings in the European Parliament at least every two months.
Vote jointly on migration
In a joint statement, the leaders said that they would vote together on issues such as migration.
"The participants have also discussed closer cooperation between the parties in the European Parliament," it said in a statement.
This includes "joint meetings and explanations of vote on key issues, such as the defense of Member States' sovereignty and attitudes towards illegal migration".
"Are there issues that divide"
What unites the parties is migration, criticism of "political correctness" and EU opposition - but there are also issues that divide them.
That is the opinion of SVT's European correspondent David Boati.
- Not least the view of Russia.
Marine Le Pen has good relations with Moscow, while, for example, Polish nationalists instinctively dislike the giant in the east, he says.
The fact that the parties are EU-critical entails certain pedagogical problems, David Boati emphasizes.
- There are difficulties in explaining increased cooperation for the "home audience" when the rhetoric in general is that the countries should take care of themselves as much as possible and give as little power as possible to Brussels.