In educational contexts there are few topics that receive as much attention from adults as children's behaviour that is seen as challenging. Challenging behaviour has been a topic in many disciplines, such as education, child psychiatry, psychology and special education. Along with the definition of challenging behaviour, we can read about social and emotional difficulties or disruptive behaviour. In this article we examine the definitions of challenging behaviour in Finnish day care. Altogether 291 professionals answered an open-ended question. The results show a wide range of individually defined meanings where the focus is mostly on children in a problem-oriented way.