Recently, various process calculi have been introduced which are suited for the modelling of mobile computation and in particular the mobility of program code; a prominent example is the ambient calculus. Due to the complexity of the involved spatial reduction, there is — in contrast to the situation in standard process algebra — up to now no satisfying coalgebraic representation of a mobile process calculus. Here, we discuss work towards a unifying coalgebraic framework for the denotational semantics of mobile systems. The connection between the ambient calculus and a coalgebraic approach which uses an extension of labelled transition systems in the representation of the reduction relation is analyzed in more detail. The formal representation of this framework is cast in the algebraic-coalgebraic specification language CoCasl.