Gone are the nipped in waists, full skirts and pretty pastel shades.
The female characters instead showcase late Sixties trends, including mini-skirts, geometric prints and monochrome outfits.
The styles placed them perfectly in 1966, where the two-hour season opener began.
Jon Hamm's character, the charismatic Don Draper, has a new wife, Megan, who is on sex kittenish form.
She looked the epitome of Swinging Sixties chic in a stylish black minidress, with her hair in a voluminous bob, as she threw her husband a surprise birthday party.
Even the makeup – heavy black eyeliner and false eyelashes – is reminiscent of the era.
Don's apartment – where Megan gave a raunchy rendition of French song Zoo Bisou Bisou while the party was in full swing – is also pure Sixties, with its white carpet, sunken living room and minimalist furniture.
Meanwhile, guests at the bash – Trudy Campbell and Jane Sterling – both show off glam beehive up dos, made popular by Sixties singer Dusty Springfield.
Even office manager Joan Holloway, played by Christina Hendricks, embraces the more daring style era with a bright fuchsia dress featuring a neckline much lower than she would normally wear.