Social work once started as volunteering and then turned into a paid profession. At present many countries try to outsource large parts of social work to volunteers. This article studies this process of voluntarisation in one large social work organisation in the Netherlands. It is based on interviews with social workers, managers and volunteers at this organisation. The study shows that voluntarisation need not go to the detriment of service quality, partly because volunteers do a good job and partly because paid social workers teach them how to do that. From a quality of work perspective voluntarisation causes concerns. Firstly because it forces paid social workers to put up with competitors who are willing to work for free and secondly, because voluntarisation often means that the core part of the job (contact between worker and service user) is outsourced to volunteers, while paid social workers are tasked with management responsibilities: coaching, budgeting, coordinating and making decisions. Because of this, we recommend a more critical stance toward voluntarisation than is currently in vogue.