The aim of this paper is to reshed some light on the broad subject of cleaning from the viewpoint of a museum conservator. One of the main reasons for cleaning or removing the varnish of a painting is a planned exhibition. This is surely not the most convincing reason for an intervention and can lead to more frequent restorations than necessary or desirable, often the fate of famous works of art. These actions are arguably the most controversial and dangerous restoration interventions that a painting will face. Such interventions are difficult because, on the one hand, the painting should not be touched if at all possible but, on the other hand, it is often unavoidable that work must be conducted directly on the painting. This means that the intervention, the effect of solvents, and any contact should stop exactly where the original paint layers begin. This cannot be guaranteed, either by traditional means or with modern materials and methods. The cleaning of a painting is more than a great physical risk for the work of art; under certain conditions it can also cause significant changes in its aesthetic appearance and perception. The success of an intervention, in particular, that of cleaning a work of art, thus depends on the cooperation between practitioners, art historians, and scientists, a partnership that is not always free of conflict. Relationships, historical facts, and questions of meaning must be collected and taken into account. This paper is intended to examine and enlighten the full range of issues encountered by professionals involved in the restoration of paintings, with particular emphasis on conservation ethics and the genesis of conservation treatment decisions.