As sensor networks operate in the real world, (real) timeliness constraints are important. These stem from both the interaction of the system with the (real) outside world, via services and applications, such as timely response to environmental conditions, as well as from the (internal) interaction among the nodes, to provide acceptable delays or freshness of data to the outside. Furthermore, sensors and actuators introduce specific constraints based on their operation and design. Thus, the network will have local as well as end-to-end temporal demands. Consequently, timeliness issues have to be addressed on the node level, dealing with trade-offs such as processing power and energy, as well as on the inter-node level, addressing the relations between network aspects such as capacity and routing and probabilities to meet end-to-end deadlines.