Shinjuku, Harajuku and Shibuya in a day

Hi, I will like to cover Shinjuku, Harajuku and Shibuya in a day. May I know if it's possible to walk from one place to another? What order should I take, ie. should I start with Shinjuku in the morning and end with Shibuya at night or otherwise? Thank you!

It's only 4 kms. An Average adult can walk through within one hour. So maybe half day is enough.

Yes. In general Sunday is "best" if you have a Sunday available.

Some of it is covered here:-
http://www.japan-guide.com/e/e3051.html
http://www.japan-guide.com/e/e3051_west_tokyo_full.html

And JNTO have some suggested walks too which include it.
http://www.jnto.go.jp/eng/location/rtg/pdf/pg-305.pdf

Enjoy your trip!

You can walk but it's normal to take the Yamanote-sen train. If you are walking maybe you can start from Shinjuku, walk throgh Meiji Shrine, go to Harajuku
and then walk besides the tracks via the Olympic stadium and get to Shibuya. But I will tell you there's not much to see between the stations. Much more efficient if you see Shinjuku, ride the train 2 stops to Harajuku, see Harajuku and the Meiji Shrine (if it interests you) and then take another stop on the train to Shibuya.