A practical approach is presented to making behaviour a concrete, first-class architectural concept. The approach overcomes the forest-tree problem that results when the only way of understanding behaviour in relation to the organizational aspect of architecture is in terms of sequences of inter-component interactions that emerge at run time (calls, messages, etc). The approach centers around diagrams called Use Case Maps (UCMs) that superimpose sets of continuous wiggly lines (representing

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... atures of causal sequences) onto arrangements of boxes (representing organizational structure). A powerful feature of the approach is its ability to express large scale dynamic situations clearly. This paper does not present UCMs for the first time, but provides new insight into their essence in relation to architectural issues, alerts workers in the field of software architecture who have not encountered them before to their possibilities, and introduces for the first time a demonstration-of-concept tool to support them.