I have a three gange box with 3 separate 12/2 runs to the panel. There are 3 corresponding 12/2 feeds to the lights.

My question is, since there are 3 separate circuits, do I need to tie all the grounds together, or only the two that make up that particular light circuit? I would assume whatever I do would also be the same for the neutral?

-All bare grounds need to be tied together
-The neutrals are treated different. Each circuit neutral should be wirenutted to any neutral related to that circuit. >>>>Not circuit neutral "A" to circuit neutral "B"<<<<<
-Now you could turn two of the circuits into a multi-circuit, but I'm not going to confuse the situation.

Thanks for the response, I'll tie all the bare grounds together, and leave the hot and neutral's separated for their respective circuit.

I am curious however as to what a multi-circuit would be?

A MWBC is a circuit where two hot conductors share one neutral.

Simple enough.

Multi circuit will have 2 hots sharing neutral, the 2 circuits must be fed by breakers on opposite phases. Has a cancelling effect. If both circuits drew 20 amps the neutral will draw Zero. If someone unknowingly switched breakers around and both were on same phase, then if both were drawing 20 amps, neutral would be carrying 40 Amps.
Goosd Luck.

Just a comment. It does set the stage for ground loops, but if you pretend that it was done in conduit and you had a metal box, that is what you would get. I don't want to go against code.
If these circuits contained grounding outlets, I'd be much more concerned about ground loops.

If CODE WOULD ALLOW, I'd be happier with insulating the grounds and keep them with their respective circuits, like they might be if using a plastic box. Then connect switches to their appropriate ground with a pigtail.

For the metal box case, do the same, except pigtail only one of the grounds to the box and the various switches. In the metal box case, only one ground handles the exposed stuff on the box and switches.

If you draw the two diagrams, the way proposed will case loops. My proposals will not..
But you have to do what CODE says. Can anybody provide a reference?

Thiis would effectively eliminate ground loops.

It is 3 lighting circuits, plastic box. I spoke with the local inspector and he confirmed that all of the ground will be made up as one, so that's how I'll do it. Thanks everyone for the comments.

U are welcome!