Drilling operations are highly professional tasks requiring special expertise and skills. Therefore, Principal Investigators (PIs) typically contract service companies to plan and execute scientific drilling. Accordingly, the PIs have the duty to oversee all operations as well as to control schedules and budget. In several projects supported by ICDP, these PIs´ tasks have been either entrusted to independent drilling consultants or to the OSG engineers. They perform as technical and managerial advisors or ‘company men’ at the drilling site and are supported by additional external experts when needed. This system allows PIs to focus on oversight issues and information to stakeholders and scientific community. In order to describe the operational and engineering tasks, this chapter summarizes some key aspects of drilling engineering and operations execution.