<P>A comprehensive introduction to interval logic and duration calculus for modelling, analysing and verifying real-time systems. The Duration Calculus (DC) represents a logical approach to formal design of real-time systems. In DC real numbers are used to model <EM>time</EM> and Boolean-valued (i.e. {0,1}-valued) functions over time to model <EM>states</EM> of real-time systems. The <EM>duration</EM> of a state in a time interval is the accumulated presence time of the state in the interval. DC extends <EM>interval logic</EM> to a calculus to specify and reason about properties of state durations. The text covers theory (completeness, decidability, undecidability, model-checking), results, as well as case studies (Deadline Driven Scheduler). </P>