This chapter describes two studies in which Palestinian assailants underwent interviews and psychological tests intended to learn about factors that influenced their decision to carry out a terrorist attack and their behaviour before, during, and after the attack. The first study examined would-be suicide bombers, a control group of non-suicide terrorists and organizers of suicide attacks, and the second study examined lone-actor assailants. Differences in personality characteristics, psychopathology and motivations for carrying out terrorist attacks were found between the various types of assailants in the two studies. Conclusions pertinent to the issue of terrorists’ risk assessment are discussed.