In this chapter, the reader is introduced to the fundamental concepts behind geological modelling with special reference on how they can impinge on ground engineering projects. The engineer should be acquainted with, and have a basic understanding of, geological time, unconformities, global geological evolution, the formulation of geological histories and the definition of terms commonly used to describe rock and superficial sequences as shown on geological maps and in reports. References to important scientific papers and textbooks that provide more information on these subjects are provided throughout this book.