We propose a graphical language that enables the specification of as-sistance systems for a given application, by means of a set of rules. We imple-mented it through the SEPIA environment, mainly composed of an assistance editor aimed at assistance designers, and a generic assistance engine able to ex-ecute the specified assistance for the target-application end-users, without a need to modify this application. SEPIA has been tested out with 71 assistance designers and more than 250 end-users.