This chapter presents two ways of associating causality semantics with en-systems. To start with, concurrency traces can be applied in a direct way to en-systems and their executions captured by firing sequences. The resulting semantical model is based on actions even though Petri nets contain also local state information which is equally significant as that provided by action occurrences. We will therefore present an alternative way of looking at causality in en-system and demonstrate that these two different ways of capturing causality in the behaviours of en-systems are consistent.