Looking for the short story where a man steps on a butterfly and changes the future. Can anyone help me out? What is the title and which book it is in? Thank you very much.

The story s "A Sound of Thunder" and is in "R Is For Rocket" (and has appeared in other collections I can't recall.)
This one seems to pop up a lot. For a while it was required reading in many public school English classes along with "The Pedestrian".
Check other threads regarding the title - new film coming out, etc...

thank u so much ! really appreciate ur response.