Here is a selection of highlights from some of winner's speeches:
Viola Davis: Best supporting actress for Fences
"Thank you to the Academy. You know, there's one place that all the people with the greatest potential are gathered. One place. And that's the graveyard.
"People ask me all the time: 'What kind of stories do you want to tell, Viola?' And I say, exhume those bodies. Exhume those stories.
"The stories of the people who dreamed big and never saw those dreams to fruition. People who fell in love and lost.
"I became an artist, and thank God I did, because we are the only profession that celebrates what it means to live a life. So here's to August Wilson, who exhumed and exalted the ordinary people.
"And, O captain, my captain, Denzel Washington. Thank you for putting two entities in the driving seat: August and God. And they served you well.
"And to Dan and Mae Alice Davis, who were - and are the centre of my universe. The people who taught me good or bad, how to fail, how to love, how to hold an award, how to lose: my parents.
"I'm so thankful that God chose you to bring me into this world. To my sisters. My sister Deloris, who's here, who played Jaji and Jaja with me. We were rich white women in the tea party games.
"Thank you for the imagination. And to my husband and my daughter, my heart, you and Genesis. You teach me every day how to live, how to love. I'm so glad that you are the foundation of my life. Thank you to the Academy. Thank you."
Mahershala Ali: Best supporting actor for MoonlightImage copyright Reuters
"I want to thank my teachers and professors, I had so many wonderful teachers, and one thing they consistently told me was that it's not about you, it's about these characters. You're a servant, you're in service to these stories and these characters.
"I'm so blessed to have had an opportunity. It was such a wonderful experience, thank you [director] Barry Jenkins, thank you Tarell Alvin McCraney [writer of the play Moonlight was based on].
"I also want to thank my wife, we just had our daughter four days ago, so I just want to thank her for being such a soldier through this process and really carrying me through it all. Thank you, peace and blessings."
Asghar Farhadi: Best foreign language film for The SalesmanImage copyright AFP/Getty Image caption Anousheh Ansari (L) appeared with ex-Nasa scientist Firouz Naderi and actresses Shirley MacLaine and Charlize Theron
The Iranian director's speech was read out on his behalf by the world's first female space tourist, Anousheh Ansari. She referenced President Trump's recent ban of immigrants travelling to the US from seven countries, including Iran.
"It's a great honour to be receiving this valuable award for the second time.
"I'm sorry I'm not with you tonight, my absence is out of respect for the people of my country and those of the other six countries who have been disrespected by the inhumane law that bans immigrants from seven countries to the US."