Conversation so far:
does an australian passport holder need a visa for spain
Australian citizens traveling to the E.U. will require a visa waiver for Europe from Australia as of the end of 2022.
when did spain become a member state of the schengen area
Spain and Portugal joined the Schengen Agreement on 25th June 1991
when was the schengen agreement signed
The Schengen Agreement was signed on 14 June 1985

Question: which countries first signed the agreement
Self-contained rewrite: which countries first signed the schengen agreement