Over the last decade or so, a new "softsensor" technology has been evolving which permits previously inaccessible process variables Is a piece of software which processes inputs from instruments that provide information related to the to be estimated. The "softsensor" unknown variables and interprets these in the context of an on-line model to arrive at the "best available" estimate of the unknown variable(s). Using as a starting point some early work conducted at the University of Utah and GS Industries, the authors describe in the current paper a general object-oriented approach to the design of softsensors for comminution systems. A generic softsensor, ComMINSens, is shown to be integrable with a variety of models in the form of object components. Applications are presented for SAG milling and ball milling circuits.