This paper covers the issues and trends associated with transitioning from an open pit operation to an underground caving mine. The decisions made on the timing of the transition affect many parameters including the Mineral Resources (Resources) and Ore Reserves (Reserves), the timing and costs associated with the studies required to support the change. Fundamental issues such as the size of the underground operation and the anticipated ramp-up are discussed as well as the options afforded by Hybrid Caves (a Sub-Level Cave (SLC) later converting to a Block or Panel Cave (BC, PC)). The economics and risks of these strategies are discussed as well as the resultant impacts on traditional financial metrics. The authors believe that an holistic approach to evaluating the transition from open pit to underground is required, not simply an open pit optimisation, followed by a transition to an underground mine. Operations generally do not allow sufficient time, or plan the pre-requisite drilling programmes early enough, to make properly informed decisions about the transition.