West Ham reached their first European final for 47 years after Thursday's 1-0 victory at AZ Alkmaar clinched a 3-1 aggregate success in the Europa Conference League semi-finals.
Pablo Fornals scored West Ham's winner in the final moments of the tense second leg to set up a clash with Fiorentina or FC Basel in the final in Prague on June 7.
The Hammers last reached a major European final in 1976 when they were beaten by Anderlecht in the Cup Winners Cup.
West Ham have not won a major trophy since Trevor Brooking's goal beat Arsenal in the 1980 FA Cup final.
They lost the 'Steven Gerrard' FA Cup final on penalties after a 3-3 draw against Liverpool in 2006.
"We're absolutely thrilled. It's a big achievement for the club, but now it's about going and winning it. AZ are very good at what they do, but I'm delighted we did it," West Ham boss David Moyes said.
"We've brought in a lot of international players to get better, but we've really struggled this season. We had to go back to what gets you wins, and thankfully we did that."
Last season, West Ham lost 3-1 on aggregate to eventual winners Eintracht Frankfurt in the Europa League semi-finals.
Moyes' side have made amends for that painful near-miss by reaching the final of a competition much-maligned in some quarters, but never again in east London.
West Ham have won 13 of their 14 games in the competition this season and will be favourites whoever they play in the final.
"We have created history. It's the first time in 47 years. It's pure emotion and happiness to get it done," West Ham midfielder Declan Rice said.
Moyes has led West Ham to top 10 finishes in the Premier League in the past two seasons, but they have struggled for much of the current campaign.
They are 15th in the table with two games left, all but mathematically safe from relegation.
Winning a European trophy would be an unexpectedly uplifting end to their troubled season.
West Ham make history
However, their victory over AZ was tarnished slightly after fans from both clubs were involved in fighting after the final whistle.
A group of Alkmaar fans appeared to get into the section holding West Ham's 700 away supporters, prompting ugly scenes before police and stewards quelled the violence.
AZ, sitting fourth in the Dutch Eredivisie, were unbeaten in their last 25 European home matches.
But their bid to reach the second European final in their history, after losing against Ipswich in the 1981 UEFA Cup, was dashed by the resolute Hammers.
Ignoring the deafening noise from the AZ fans who set off red flares before kick-off, it was West Ham who seized the initiative.
Jarrod Bowen fired just wide from the edge of the area before Lucas Paqueta went even closer with a curling strike that clipped the far post.
Unable to establish any momentum for much of the first half, AZ almost snatched the lead against the run of play just before the break.
Vangelis Pavlidis's flick flashed dangerously across the six-yard box before Yukinari Sugawara's goalbound effort was blocked by Nayef Aguerd moments later.
That was the signal for a strong spell for the hosts after half-time, with Sven Mijnans tested Alphonse Areola with a low drive from the edge of the area.
Aguerd survived a VAR check following Alkmaar appeals for a penalty after his risky sliding tackle on Pavlidis.
And in stoppage-time, Fornals sprinted clear of the tiring Alkmaar defence to slot a cool finish past Ryan as West Ham were finally able to celebrate a memorable success.
