This handbook is mainly concerned with the sequence of events that occur between the discovery of a mineralized deposit, through its classification as a mineral resource, on to the determination whether and to what extent that it constitutes a mineral reserve (mineral resource that may be exploited at a profit). In recent years, the miner’s role has been less concerned with exploration geology and ore reserve estimation. The latter, once the responsibility of a professional mining engineer, is now typically performed by a “geoscientist” (geologist, geological engineer, geochemist, or geophysicist). The change has not occurred without problems. The root cause is commonly believed to be that geo-scientists were not regulated by a professional body and hence could not be held legally responsible for their actions. Hence, this chapter does not provide full consideration for geology and reserves, but deals more with driving entries for underground exploration, which is the domain of the miner.