This chapter examines encounters around mental illness that played out within mandate Palestine’s hybrid legal system. Issues of mental competency and legal responsibility were debated across civil and religious courts, but this chapter focuses on the criminal courtroom and criminal insanity defences. Criminal insanity defences forced mandate judges, medical experts, and lay witnesses to debate what forms of behaviour and thought were evidence of mental illness, and what should, by contrast, be considered normal, ‘rational’, and therefore punishable for a given defendant. Through a close reading of two exemplary cases, this chapter moves beyond the historiography’s focus on cultural difference to highlight how different bodies of knowledge – psychiatric, social, and folkloric – were put to work to define the ‘normal’ in relation to other axes of identity like age, class, and gender. A third case, which played out against the backdrop of the Palestinian great revolt, meanwhile reveals how understandings of the ‘normal’ could be warped by wider political circumstances, with life-or-death consequences for defendants.