The Connecticut Department of Mental Health began creating assertive community treatment teams in 1987. The authors describe the approach taken by the department in defining the assertive community treatment model, in creating new assertive community treatment teams, and in monitoring the creation and functioning of these teams to ensure that fidelity to the assertive community treatment model is maintained. Assertive community treatment teams can be created even in the absence of funding for new staff by reconfiguring current community-based staff and by moving staff from state hospitals to the community. Preliminary data from a randomized trial in Connecticut comparing assertive community treatment with high-quality case management in areas with an array of community services indicated that the intended models were replicated, with variations in practice style across programs. Clients in assertive community treatment were in the hospital about half as often as clients in standard services and were also less likely to be without a permanent residence. Training and ongoing monitoring of assertive community treatment teams are necessary to detect practices that diverge from the intervention model so that corrective action can be taken.