This chapter aims to present the general context of a measurement system and basic concepts of measurement and related terms. The presentation develops according to a step-by-step, top-down strategy, which progressively characterizes measurement as (i) an empirical process, (ii) designed on purpose, (iii) whose input is a property of an object, and (iv) that produces information in the form of values of that property. These are proposed as necessary but not sufficient conditions for a process to be identified as a measurement: as such the contents of this chapter should be uncontroversial to be read and accepted by most, if not all, researchers and practitioners.