The chapter provides introductory background information on all relevant fields (Games-based learning, Mobile devices, Mobile entertainment, Mobile education, Behavioural psychology) and showcases a small number of mobile devices based serious games and applications to support the claim that such games can be implemented for this device type. It then introduces formal propositional logic and suggests the use of a formal language to express statements about games and events in games. The next section is referencing to established guidelines from the field of behavioural psychology and provides an formalism (based on the content of the previous section) that allows the unambiguous definition and evaluation of behaviour in the context of a game. The chapter is targeting the large stretch of vagueness (definition of the behaviour under investigation, design of a game to evaluate such behaviour, collection of data/profiling and finally the interpretation of this data) that is found in almost all existing work concerned with human game playing behaviour. The contribution of the chapter is the introduction of a formalism which removes the vagueness and ambiguity from parts of this stretch. Ideally the only subjective part of the evaluation of human game playing behaviour is to be found in the final interpretation of the data, and the formalism allows for this reduction of vagueness (given that it is well constructed and tailored to the investigation at hand).