Tobacco and cigarettes are only sold to people 18 years or older. You can buy cigarettes in convenience stores and supermarkets in Denmark. 

In Denmark it is against the law to smoke in indoor public places, except in specially equipped smoking booths. This includes restaurants, cafés, bars, all forms of public transport and taxis. You may smoke in bars or cafes with a license to sell alcohol, if they are smaller than 40 square meters in size. Hotels determine their own smoking rules but most hotels are non-smoking.