The overall aim of this thesis was to study participants' understanding of clinical cancer trials, and their motivation for participation. Of particular interest was the question of whether the patients hoped for a cure resulting from the trial. The thesis was based on four studies and used three methods: interviews, a questionnaire, and empirical bioethics. The results of Study I indicated that the participants in phase 1 trials understood most of the information provided, but were unaware of both the very small potential for treatment benefit, and the risk of harm. Patients in phase 3 trials had a good understanding of the trial, except regarding side effects and their right to withdraw. Some found it hard to ask questions and felt they needed more information (Study III). The participants in phase 1 trials were strongly motivated by the generally unrealistic hope for therapeutic benefit (Study I). When the chances of a cure are minuscule, as for participants with end-stage cancer in phase 1 trials, hope can play an important, positive role and offer meaning to one’s remaining life. However, hope for an unrealistic outcome could also deprive patients of an opportunity to spend their remaining lives, as they would otherwise choose (Study II). The participants in phase 3 trials indicated that their motivation for participation was multifaceted; the most common motivations included hope of therapeutic benefit, altruism, access to extra clinical examinations or better care, and a wish to repay society for the help they had received (Study III). After stratifying and analysing the motivation data by gender, age, education and previous experience of trial participation, males and those aged ≥65 years were significantly more motivated to participate out of a desire to reciprocate the help they had received, either because of a sense of duty or because their families or friends considered that they should attend (Study IV). In conclusion, the informed consent process seems to work relatively well, with good results within most subgroups. However, patients with end-stage cancer who are participating in phase 1 trials are a vulnerable group as they have very little potential for treatment benefit coupled with a tangible risk of harm.