Yes, for residence permits based on employment, a signed work contract is mandatory. The Swedish Migration Agency requires this to ensure that your salary, employment conditions, and insurance coverage meet national labor standards. Without a valid work contract, you cannot apply for a residence permit to work. However, other residence permits such as study, family, or job-seeker permits do not require a work contract but have their own eligibility requirements. Therefore, while employment-based permits strictly require a contract, the necessity depends entirely on the category of residence permit you are applying for.