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In London Marathon week, BBC Sport is launching the #IRunFor campaign for the 2017 summer of athletics.
The event mixes local runners with some of the world's best, all tackling the same course for their own reasons.
It could be to win, for a personal best, for donations or awareness of a cause. The #IRunFor campaign will focus on their stories and reasons they run.
The London Marathon, which will be live on BBC One on Sunday, 23 April, is the first in an action-packed summer of athletics.
The Great Manchester Run, Great North Run, Great Scottish Run and Cardiff Half Marathon are just some of the other mass-participation events that will be covered by the BBC and feature in the #IRunFor campaign.
The campaign will carry on across the World Athletics and Para Athletics Championships and beyond.
As well as hearing from you, the campaign will also ask elite athletes participating in the Manchester City Games, World Para Athletics and World Championships what their motivation is.
So, the next time you are pounding the streets think about why you do it, and be ready because we'll be asking you to be part of our #IRunFor campaign very soon.
And if you have good reasons but still haven't managed to take up running, we've got a guide to help you start.
Whether you're running an international championship race or out for a weekly jog, we all have a reason to run.