Oscars Fashion: Emma Stone, Rihanna, Amal Cooney the Next Style Icons

Ah, the Oscars. With fashion's and Hollywood's biggest night upon us, Glamour invited author Michael Callahan, an expert in old-Hollywood fashion and author of the new book Searching for Grace Kelly, to uncover what timeless style means today—and how contemporary red carpet stars measure up to icons past.

Lauren Bacall, Jackie O, and Grace Kelly understood the art of chic restraint in their day.

Hollywood and fashion have long made for loving bedfellows. Who could forget Audrey Hepburn's little black Givenchy dresses, Lauren Bacall's plunging columns, or Grace Kelly's namesake Hermes bag? And yet while it was once fairly easy to declare an actress eternally chic, the task has become much less obvious in today's Instagram-my-outfit generation. What now separates the trendsetters from the sartorial revolutionaries? Of the red carpet stars today, whose style will transcend? What makes an actress worthy of a spot alongside the icons of yesteryear?

The secret is in one word: restraint. It's the sheer power of holding back, of keeping one's own counsel, of mystery. (Picture Kelly's Frances Stevens in To Catch a Thief, thoroughly discombobulating Cary Grant.) That's what Grace and Audrey and even Jackie O had in common. You didn't know everything they thought or did, because they didn't want you to know. Whether in beautiful evening clothes or their button-down sleeveless blouses and jeans, they held something back, gave us enough room to project our own fantasies onto them. There is so little left to the imagination anymore, so little we don't know.

One roadblock for stars looking to capture this enduring style is the pace of fashion trends today. With fashion shows more visible to the world, the pressure is on designers and tastemakers to change things up quickly and drastically. Not counting haute couture, designers are now creating four full-line collections a year and are constantly challenged to invent or reinvent new trends. These trends are a funny thing: As with presidential administrations, only the passage of many years can unearth lasting style. This spring, it's all about graphics, military jackets, and, God help us, the return of the '70s. (Why? Why?) Are any of these trends likely to be with us 10, 20, 50 years from now? Perhaps. Fashion fiddles, but it never burns—although sometimes I wish it would.