  This paper addresses the problem of scalability for a cell-free massive MIMO
(CF-mMIMO) system that performs integrated sensing and communications (ISAC).
Specifically, the case where a large number of access points (APs) are deployed
to perform simultaneous communication with mobile users and monitoring of the
surrounding environment in the same time-frequency slot is considered, and a
target-centric approach on top of the user-centric architecture used for
communication services is introduced. In the paper, other practical aspects
such as the fronthaul load and scanning protocol are also considered. The
proposed scalable ISAC-enabled CF-mMIMO network has lower levels of system
complexity, permits managing the scenario in which multiple targets are to be
tracked/sensed by the APs, and achieves performance levels superior or, in some
cases, close to those of the non-scalable solutions.
