Lots of chat on Twitter as the stars parade in the rain:

• Emmy Potter tweets, external: "JK Simmons' fedora feels like a nod to his past when he was a wise guy in Guys and Dolls on #Broadway. Luck be a lady tonight."

• H Dizzle, external: "Michael Keaton is starting to look older than Clint Eastwood."

• Sarah Maclean, external: "Remember what I said about white? Oh, Benedict. Handsome devil."

• Keira Soleore, external: "Cumberbatch, oh no! That off-white jacket with the white shirt? NO!"

Tim Masters
Entertainment correspondent in Los Angles

Much of chat here in the press room is around the acting categories.

Three of them appear to be "locked" - with Julianne Moore expected to win best actress for Still Alice, and JK Simmons and Patricia Arquette to win for their supporting roles in Whiplash and Boyhood respectively.

So the big fight is for best actor with Eddie Redmayne and Michael Keaton being talked up as the main contenders in a very competitive field. Or does Bradley Cooper have the prize in his sights for his role in American Sniper?

Pret a Reporter tweets, external: "How gorg is the #Oscars green room that Julianne Moore helped design??"

Image source, Rodger Davies/Architectural Digest

Selma director Ava DuVernay has tweeted, external a lovely video capturing the final moments of filming on the movie.

"I never shared this. I saved it for today. A special outtake of my hero. I love you, David. You are my best actor," she said.

Watch the video, external.

Image source, Getty Images

The Academy tweets: "It's no @Pharrellhat, but #JKSimmons hat is pretty fun."

Image source, Reuters

Lupita N'yongo's custom-made dress has 6,000 pearls sewn onto it. Bet she can't wait to put her PJs on (and lose the bodyguards).

The actress won the best supporting award last year - and became an overnight star and fashion favourite.

Best supporting actor nominee Mark Ruffalo tweets, external: "Preview. Lots of love to all. Thanks for all the support and kindness."

Image source, Instagram

Oscars producer Craig Zadan tweets, external: "Rehearsals done. We are locked. No more changes. Hour and half we go live. And then it all begins. And in live television it just happens."

Image source, Reuters

Elton John has dodged the ceremony and gone straight to (his own) party.

At least he has Nile Rodgers for company, and I guess a few more will turn up later...

Best actor nominee Michael Keaton grabbed Selma star David Oyelowo on the red carpet.

Image source, Getty Images

Image source, Getty Images

Best actress favourite Julianne Moore has arrived and she's wearing white.

She's in good company this year with Marion Cotillard, Lupita N'yongo and Patricia Arquette all favouring white frocks.

Tim Masters
Entertainment correspondent in Los Angeles

I'm backstage at the Oscars with several hundred members of the world's press. We are gathered in a giant hotel suite adjacent to the Dolby Theatre.

Tonight's Oscar winners will be brought here after they have made their speeches on stage.

Never have so many journalists looked so smart. It's like we are all about to attend a grand ball. Sadly no photography is allowed, but I'm in my trusty tuxedo.

Best song nominee John Legend is promising to do "something special" with his performance of Glory, from the film Selma, at this evening's ceremony.

All the nominees will perform at the ceremony, including British star (and Voice mentor) Rita Ora and Sara and Tegan of 'Everything is Awesome' fame.

Oscar host Neil Patrick Harris adjusts the tie of his husband, David Burtka.

Image source, Reuters

Best actress nominee Rosamund Pike arrived in a striking red dress.

Image source, Getty Images

Image source, Reuters

It's raining on the red carpet, but it's not putting a dampener on the stars' high spirits - best actor nominee Eddie Redmayne says it feels "beautifully British".

He said he felt "relatively relaxed" compared to when he attended the ceremony in 2013 where he performed a song from Les Miserables. "Last time I had to sing, so tonight feels relatively chilled in comparison," he said.

Last year's host Ellen DeGeneres is settling in for the night, this time at home. She tweeted, external: "Tonight's the night! The stars, the gowns, speeches, and the thing I'm most looking forward to - watching from my sofa."

Jaime Gonzalez
BBC Mundo, Los Angeles

BBC Mundo's Jaime Gonzalez tweets, external: "Live from the red carpet at the #Oscars2015."

The Academy tweets: "No matter who "wins" tonight, we all win when people make great movies."