where can you see what list a lead belongs too?

Hi Lauren, if you look in the activity log of a specific record, you should be able to see what list they were added to or imported to.

thanks Dory, I've had a look at the activity long and for some reason there is nothing there. 

I thought that would be the best place for it but I wasn't sure if there was a field.

Have you tried pulling a report using the "member of list" filter?

thanks Kristen, I have tired that but we have a lot of static lists in Marketo, I was hoping there would be a quicker way.  I think it's going to be a case of narrowing it down one by one with the report as you said.  

If this is something that you do often, you could always create a tag type for them but that would only work if you're importing lists from similar sources repeatedly and are looking to see which lists are bringing in the most leads or whatnot.