The concept 'Minimally Invasive Dentistry' can be defined as maximal preservation of healthy dental structures. Within cariology, this concept includes the use of all available information and techniques ranging from accurate diagnosis of caries, caries risk assessment and prevention, to technical procedures in repairing restorations. Dentists are currently spending more than half their time replacing old restorations. The main reasons for restoration failures are secondary caries and fractures, factors that are generally not addressed in the technical process of replacing a restoration. Prevailing concepts on minimally invasive dentistry seem to be 'product or technique-motivated', challenging one technique or product with another, rather than focusing on a general concept. New knowledge of caries progression rates has also led to substantial modification of restorative intervention thresholds and further handling of the disease. New diagnostic tools for caries lesion detection, caries risk assessment and focused preventive treatments have decreased the need for early restorative interventions. In parallel to this, new techniques for cutting teeth and removing decay have evolved. This paper focuses on describing minimally invasive dentistry in cariology from a conceptual perspective, relating to clinical caries diagnosis, restorative intervention thresholds and operative procedures, with special reference to survival of tunnel and slot restorations and to repair vs. replacement of defective restorations.