: This paper uses category theory to emphasize the relationships between Mealy, Moore and Rabin-Scott automata, and the behavioural automata are used as a unifying framework. Some of the known links between Mealy, Moore and RabinScott automata are translated into isomorphisms of categories, and we also show how behavioural automata connect to these automata. Considering the distinction between final and sequential behaviours of an automaton, we define a sequential version of Mealy automata and study its relationship to behavioural automata. Key Words: Mealy, Moore and Rabin-Scott automata, semiautomata, behavioural automata, final and sequential behaviours of automata, category theory