This chapter aims to introduce the reader to the fundamentals of signal based traffic regulation, and trace the progress made so far in the attempt to render signalisation of urban areas a truly proactive feature of the infrastructure, capable of adapting to — and in some cases positively influencing — the road user demand. The main features that characterise a signalisation plan are first formalised, so as to introduce the basic principles for the optimal management of conflicting manoeuvres at a single intersection in relation to specific traffic conditions. An overview is then given of the most prominent strategies used to further optimise signalisation plans in sight of complex network-wide objectives, or to enact specific traffic management policies, following a distinction between offline Signal Setting processes used to design pre-timed plans, and online Signal Control methods relying on real-time data to adapt dynamically to the immediate circumstances.