chickens moulting?

Do you know anything abut chickens moulting? I just started with the chickens last spring, so I haven't had the experience of moulting yet. I have 4 hens: one Black Astralorpe, one Silver-Laced Wyandotte, one New Hampshire Red and one Brown Single-Comb Leghorn. All of them have been laying wonderful large eggs regularly - up to last week. They all seem to have an abundance of feathers on the ground, especially the Australorpe who is starting to look a bit scraggly. They stopped laying eggs completely this past week. Is this a part of moulting ? How long should this moulting last?

Thanks for your help,

Cindy Lou