The informal summit will discuss ways to remove the final obstacles for an EU-UK divorce agreement and plan future ties.
As Brussels and London have less and less time to agree on Brexit conditions, EU leaders might need to hold the last meeting in November, despite plans to finish negotiations in October. Any agreement will also have to be ratified by the parliaments of the UK and EU member states and the European Parliament.
Without an agreement, Britain will have to leave the EU in late March without any plan.
In Salzburg, EU leaders will also discuss migration challenges as some southern European states are trying to convince member states to share the burden of immigrants coming to Europe from the Middle East and African countries.