Get identical elements in two lists with LINQ

Question

I'm pretty novice with LINQ, and I usually use only Where() function.

Let's suppose that I have two lists with objects of the same type, l1 and l2.

My actual code looks like this :

int i, j;
for (int i = 0; i < l1.Count; i++)
{
    for (int j = 0; j < l2.Count; j++)
    {
        if (l1[i].Equals(l2[j]))
        {
            //Do stuff
        }
    }
}

I have the feeling that I can improve my code with LINQ, by getting all "duplicate" elements in l1 and l2. Have you any idea of how ?

Thank you in advance and sorry for my bad english.