This thesis defines labour law in the Republic of Croatia with a special focus on the work ability of workers, primarily the decreased work ability and loss of work ability, and the rights in such cases. The first chapter gives a general interduction to labour law, lists its sources, and provides a detailed definition of the employment relationship and employment contract along with their characteristics. The second chapter is more closely focused on the assessment of temporary incapacity for work and its distinction from the assessment of work ability. The third chapter defines the concepts and causes of the decreased work ability and loss of work ability and mentions the protection of workers who have decreased work ability with remaining work ability. Furthermore, the fourth chapter explains the rights regarding termination of employment and severance pay in cases where there is a decreased or loss of work ability, while the fifth chapter lists the rights from pension insurance. The sixth and final chapter focuses on examples from court practice, especially those concerning the right to employment in other jobs, termination of employment and severance pay in cases where there has been a change in work ability compared to a completely healthy person.