Step traces are an extension of concurrency traces where each equivalence class (step trace) consists of sequences of steps rather than sequences of actions. Relationships between individual actions are defined statically as the parameters of step alphabets. Allowing only some of the possible relationships between actions leads in a natural way to subclasses of step alphabets. This chapter presents a classification of several subclasses of step alphabets and investigates order structures representing the causal dependencies in the corresponding step traces.