I want to put down mulch where there is grass now. Do I Remove grass??

I would or grass could grow through or put down black plastic first

It would be in your best interest to remove the grass,line the area with landscape fabric and then newspapers and mulch.

Yes remove the grass, then put down landscape fabric. I wouldn't personally use the newspaper layer as suggested by Janet Pizaro, because it will promote mold. You should put a minimum of 3 to 4 inches of mulch, then if it needs refreshing next year you can use less.

I have had great results in the past using newspaper right on top of the grass. For instance I created a large tree ring using 3-4 sheets of newspaper overlapping a little in a circle and held down along the outer border with bricks to make an edge. Wetting the newspaper after you put them down is easier than trying to handle sheets of wet newspaper. Put your mulch on top. I like this technique because there is no digging or herbicides, I use a lot of newspapers I have to get rid of anyway, and you are done in about three hours.

You can dig it out! Time consuming. But you can also put down black plastic for a few weeks, and let the heat of the sun kill the grass.