We study the behavioural theory of Cardelli and Gordon's Mobile Ambients. We focus on a standard contextual equivalence, reduction barbed congruence, and we prove a context lemma that allows the derivation of contextual equivalences by considering only contexts for concurrency and locality. We then go further and give a characterisation of reduction barbed congruence over arbitrary processes, in terms of a labelled bisimilarity defined over a restricted class of processes, called systems.

The characterisation is used to investigate the algebraic theory of processes by proving a collection of algebraic laws.