Publisher Summary This chapter deals with the basic terminology and the processes associated with petroleum engineering. Petroleum engineering is principally concerned with building static and dynamic models of oil and gas reservoirs. The chapter lists some key parameters that these models aim to determine. It is necessary to construct a dynamic model of the field to predict the hydrocarbons that may be actually produced from a field. A field development plan (FDP) concerns with the production of hydrocarbons. Once an FDP has been approved, the drilling campaign consists of well proposals, in which the costs, well trajectory, geological prognosis, and data-gathering requirements are specified. The petrophysicist plays a part in the preparation of the well proposal in specifying which logs need to be acquired in the various hole sections. Logging while drilling (LWD), wireline openhole logging, wireline cased hole logging, and pipe-conveyed logging are the basic log types that are run. An oil company sets up logging contracts with one or more contractors for the provision of logging services. A logging program is prepared at the FDP stage in a field development. Tool failure and stuck tools are the things that are considered during operational decision-making. Particularly during the exploration phase of a field, coring presents an important means to calibrate the petrophysical model and gain additional information about the reservoir that is not obtainable by logs during the exploration phase of a field. A mud-logging unit is set up on the ring during drilling of a well that monitors the drilling parameters and provides information to the petroleum-engineering department for evaluation process. Testing is done at the end of logging that approves the running of a well.