I know but one freedom, and that is freedom of the mind.—Antoine de SaintExupéry Terrorists seek to wreak havoc in society, whether they are the self-proclaimed Muslim marauders who rammed their vehicles into revellers on London Bridge and Borough in the United Kingdom or the far-right fanatic who shot and killed Muslim worshippers in a mosque in Quebec, Canada. But what do we know about the conflicting and terrorizing forces that often operate in the minds of those who perpetrate heinous and horrific atrocities such as these? What are the psychological determinants and social influences that could drive people to carry out such abhorrent and abominable activities? This chapter aims to answer these questions and provide mental health practitioners with a map to help them navigate through the precarious territory of the minds of those who perpetrate terrorism. In Section 1, we discuss, describe and delve into some of the major psychological determinants and social influences of violent extremism. In Section 2, we offer insights into the pernicious phenomena of undue influence, brainwashing and mind control, and the roles that each potentially plays in the cognition, character and conduct of members of destructive cult organizations. We conclude with clinical considerations for mental health practitioners as well as suggestions for how to stymie the proliferation of dangerous mind control cults of all kinds.