Yes, there are formal nights on Celebrity cruises®. We call them Evening Chic nights, and they’re simply an opportunity for you to dress up and feel your best. On cruises of six nights or less, there will be one Evening Chic night, and on cruises of seven nights of longer, there will be at least two.

In terms of dress code, think attire that is sophisticated yet relaxed. For women, this could be cocktail dress, or a skirt or smart jeans and top. Men can wear trousers or dark jeans with a button-down shirt, as well as blazers. 
Evening Chic nights are completely optional. The dress code is enforced in the main dining room, but if you’d prefer not to take part, there are plenty of dining alternatives and in-room options where you’re welcome to wear more casual attire. On all other nights, you’re encouraged to wear smart/casual clothing you feel comfortable in.