In a recent paper, Bentzen proposes a semantically characterised logic called Action Type Deontic Logic, where normative concepts are applied to action expressions, rather than propositional statements. The logic offers solutions to many of the paradoxes of deontic logic. In particular, Bentzen's semantics solves many puzzles involving the interaction of permission with conjunction and disjunction. One of the reasons for these positive results is the assumption that agents always act according to norm. This assumption means that only agents with ideal behaviour are modelled; there is no possibility for norm-violation. In this thesis, proof techniques and decision procedures for Action Type Deontic Logic in the style of semantic tableau are investigated, and soundness, completeness and termination results are obtained. In order to account for the possibility of norm-violation, a new semantics based on a generalisation of Action Type Deontic Logic models is proposed. The new semantics keeps the possibility of norm-violation open, while many of the virtues of Action Type Deontic Logic remain.