The overall aim of this thesis was to study the daily process of coping, potential prognostic factors for recovery and evaluating an individually tailored behavioural medicine intervention in the acute stage of Whiplash Associated Disorders (WAD). The studies comprised three samples of patients with acute Whiplash Associated Disorders (WAD). All patients were included within the first month after the whiplash occurrence and were recruited from hospital emergency wards in six Swedish communities. Study I and II included 51 participants generating 260 daily coping diaries (WAD-DCA) during seven days in the acute stage of WAD. In Study I daily stressors and primary appraisal were analysed and in Study II patterns between stressors, appraisals, coping strategy profiles, daily activity level and well-being were described. The results showed a large variety of situations that the individuals perceive as stressful, not only pain itself. High self-efficacy was associated with high degree of physical/mental well-being. Threatening stressors and catastrophic thoughts were associated with low degree of physical and mental well-being. In Study III potential prognostic factors for good as well as poor recovery were studied more closely in a mildly affected sample (MIAS) (n=98) from within the first month after the accident up to one year later. Pain-related disability at baseline emerged as the only indicator of prognosis after 12 months in MIAS. Study IV (n=55) was a randomised control study, were current clinical recommendations of standard self-care instructions (SC) for the management of acute WAD was compared to an individually tailored behavioural medicine intervention delivered via Internet or face-to-face. The results showed that SC was not as effective as the behavioural medicine intervention. By early identification of situation-specific factors and potential behavioural (physical, cognitive and affective) determinants of activity performance, it seems possible to tailor a self-management intervention that decreases pain-related disability, fear of movement and catastrophising and increases self-efficacy. The use of innovative methods such as the Internet of distributing treatment interventions showed to be a good alternative to more traditional forms. The results of this thesis uncover new insights in understanding the individual’s specific perspective as applied in a behavioural medicine approach in acute WAD.