This is one of the most memorable retro looks ever worn by a modern celebrity. It's vintage yet modern and perfectly executed. The accompanying makeup is spot-on, and it goes perfectly with Klum's gown. And it was easy (albeit expensive) - Klum just popped on a custom-made hairpiece. See more Heidi Klum hairstyles.

While the amazing Ms. Klum rarely flubs, here she missed the mark. This sixties-inspired updo is so over-worked and glazed into place, it looks like a petrified bale of hay. It's downright intimidating. If your hairstyle can be used to break open walnuts, you've gone too far.See more Heidi Klum hairstyles.

Here Scarlett Johansson demonstrates exactly how to hint at an era with a style. There's just enough teasing at the crown to suggest the early seventies. Any more would have been too much. The look is intensely stylish without trying too hard. See more Scarlett Johansson hairstyles.

Know what makes a given retro style beautiful. Forties-inspired head-hugging waves, a la Veronica Lake, are a showcase for shiny healthy locks. If your hair is limp with damage, and needing a color touch up, as seen here, those flaws undo the glamour of your 'do without mercy. See more Scarlett Johansson hairstyles.