T-shirts are about as basic as basics get. But the best T-shirts for men go beyond fashion fundamentals; they can play the lead just as well as the supporting role. Save for daring feats of shirtlessness, the T-shirt is the foundation of practically every great outfit, whether it's taking the spotlight with a classic pair of blue jeans and sneakers, hiding under a flannel shirt or hoodie, getting dressed up with a luxuriously louche suit, or soaking up your hard-earned sweat in a swishy gym get-up. Before brazen graphic tees and high-end Supima cotton splurges existed, the T-shirt had humble beginnings as a basic undergarment. If you're attempting to protect your nice dress shirts and sweaters from the funk of your sweat glands, or simply need a warm base layer to keep the frigid air out, undershirts are designed to play a supporting role so the rest of your outfit can truly shine. You’ll find ‘em in a range of materials like waffle-knit thermals and temperature-regulating Merino wool—in addition to plain ol’ cotton jersey. But FYI: most good undershirts will lean closer to the slim-fit end of the silhouette spectrum.