This paper describes the evidence base for Dyadic Developmental Psychotherapy as an evidence‐based and effective family‐therapy treatment for child with reactive attachment disorder and complex trauma. The paper summarizes the extensive empirical literature that describes the effectiveness of such dimensions of Dyadic Developmental Psychotherapy as affect arousal and regulation, gradual exposure to trauma, parent education and consultation, explaining how the past may be continuing to affect present behaviour, forming and maintaining a therapeutic relationship through therapist acceptance, affirmation, empathy and various other dimensions. The paper presents several generally accepted criteria for determining evidence‐based practice and evidence‐based treatment and demonstrates how Dyadic Developmental Psychotherapy meets those criteria. These criteria include those developed by Saunders et al., the UK National Health Services system and the US Preventative Services Task Force system for ranking the quality of evidence. Finally, the paper describes several misrepresentations and inaccurate statements by Mercer and Pignotti in their note and corrects these errors of analysis and judgement.