For women it’s pretty easy, you can wear whatever you want with a cardigan, starting with a basic cotton T-shirt and down to the most precious silky blouse. Also, a nice linen shirt tastefully unbuttoned at the top will look great with a classic cardigan. As for men, the type of shirt you should wear with a cardigan depends on the occasion. For a casual outing, a T-shirt with a funky print will do. However, if you need to look more classy, you might want to put a regular shirt under a cardigan. If your cardigan goes up to the collarbone, make sure the collar of the shirt is nicely tucked under the sweater, for a more modern look. Let it show, but just a bit. For a V-neck cardigan choose a shirt with a small rectangular collar or no collar at all.