Assertive Community Treatment (ACT) is one of the oldest and most researched evidence-based practices(EBPs) for treating people with serious mental illness. The Maintaining Fidelity to ACT: Current Issues and Innovations in Implementation guide reviews ACT principles, summarizes contemporary issues impacting ACT teams, and examines aspects of ACT implementation when extending the model to specific populations and settings. The goal of this guide is to ensure continued efficacy of ACT by reaffirming its principles while promoting awareness of new developments that providers may want to consider when implementing the model.