Daytime: Casual all the way, with most people wearing shorts and T-shirts inside the ship and bathing suits and cover-ups outside on the pool deck. Some activities, such as the racetrack and laser tag, require closed-toe shoes.
Evening: Anything goes at night on Norwegian, which carries an all-day casual dress code. You'll see people wearing any range of outfits, from capris and blouses to maxi dresses and going-out attire. In the Manhattan Room main dining venue and in the upscale specialty restaurants (Onda, Le Bistro, Cagney's, Ocean Blue), you'll need to dress up a bit -- slacks, nice jeans, dresses, skirts and tops for women, and nice jeans, slacks, collared shirts and closed-toe shoes for men.
Norwegian Encore has no formal night, but there is Norwegian's Night Out, where men usually wear long pants (dark jeans are fine) and collared shirts, and women put on dresses or nice skirt-and-blouse combos. Norwegian does also have some themed events -- popular ones include the glow party, country night and various decade-themed parties.
Not permitted: Bathing suits are allowed in the buffet and outdoor venues, as long as you have a cover-up and shoes on. Tank tops for men, flip-flops, baseball caps, visors and jeans that are overly faded, with holes or tears and worn below the hips are not permitted in the main dining rooms or specialty restaurants. Kids under 12 can wear nice shorts into all restaurants.
For more information, visit Cruise Line Dress Codes: Norwegian Cruise Line