Temporal aspects play a major role within clinical guidelines. Temporal issues arise when considering both guidelines per se, and the application of guidelines to specific patients. As a matter of fact, guidelines per se specify different diagnostic and\or therapeutic patterns, and temporal constraints on the intended times of execution of the actions they contain are an intrinsic part of guidelines themselves. Moreover, guidelines must be executed on the basis of patients' data, which are intrinsically temporal data (consider, e.g., the time when symptoms hold). Devising suitable representation formalisms to properly model such pieces of temporal information is a challenging task, for which several solutions have been proposed in the last years. Besides representation formalisms, temporal reasoning methodologies are also needed. Temporal abstraction is needed in order to infer abstract temporal data (as described in guideline action conditions) from "raw" timestamped patient data. Moreover, temporal constraint propagation is also needed, both at acquisition and at execution time. During acquisition, temporal constraint propagation is used to detect whether the temporal constraints in the guideline are consistent. At execution time, it is needed in order to check whether the actual time of execution of actions has respected the temporal constraints in the guideline, and to detect which are the next candidate actions to be executed, on the basis of the temporal constraints in the guideline. This chapter sketches some of the most important recent results about the above issues.