what's the difference between "fill in" and "fill out"? correct me if I'm wrong, but I think both forms can be used as the same meaning, but for me, "fill out" it's more used when you've finished the action of filling the questionnaire (e.g. I got the paper and I filled it out -- completely) and "fill in" more used when you haven't started the action yet (e.g. please fill in the form). I think it also depends on the country, let me know which one is more used in your country (native English speakers) thanks.