Your general terms of employment are predominantly regulated by collective agreements concluded by the social partners: the trade unions and employer’ associations.
The trade unions act and negotiate on your behalf to secure you the best possible salary level and working conditions. Being a member of a trade union is very common in Denmark and can provide you with a series of employment- and career-related legal support and services you may need e.g. guidance regarding individual employment contract, salary, industrial accidents and injuries.
In order to sign up you are not obligated to become a member of a trade union.
For more information and for trade unions with English websites, please have a look at: https://www.workindenmark.dk/Working-in-DK/Trade-unions and http://www.worktrotter.dk/component/content/article/177-trade-unions-work-copenhagen-denmark.html