Some people struggle desperately with the decision... others have known since they were five years old.
With so much emphasis put on the first dance song, the pressure to get it right is immense.
Well, if you're looking for a little inspo - Spotify has gone to the trouble of ranking the most popular first dance songs in Ireland.
And in at number one is our very own Kodaline with The One, followed by an absolute classic - At Last by Etta James.
Also in the top three is Jason Mraz with I Won't Give Up, and of course Ed Sheeran is in there with his 2014 Thinking Out Loud.
Here's the full list of the top twenty most popular first dance songs in Ireland.
1 Kodaline The One
2 Etta James At Last - Single Version
3 Jason Mraz I Won't Give Up
4 Ed Sheeran Thinking Out Loud
5 John Legend All of Me
6 Ellie Goulding How Long Will I Love You - Bonus Track
7 Al Green Let's Stay Together
8 Elbow One Day Like This
9 Ray LaMontagne You Are the Best Thing
10 The Lumineers Ho Hey
11 Elvis Presley Can't Help Falling in Love
12 Jack Johnson Better Together
13 Eric Clapton Wonderful Tonight
14 Christina Perri A Thousand Years
15 Ellie Goulding Your Song
16 Adele Make You Feel My Love
17 The Wannadies You And Me Song
18 Glen Hansard Falling Slowly
19 Snow Patrol Chasing Cars
20 Paul Weller You Do Something To Me