This Pilot Randomized Controlled Trial (RCT) overall aim is to establish the safety, feasibility, acceptability and preliminary effects of a body-oriented psychotherapy, Somatic Experiencing (SE), on social functioning and mental health among adults with a history of Child Maltreatment (CM) and symptoms of posttraumatic stress disorder (PTSD) or complex posttraumatic stress disorder (CPTSD). Participants will be randomized either to an SE-group (n=25, psychoeducation, and information about treatment possibilities + 15-session SE treatment) or to a control group (n=25, same psychoeducation and information about treatment possibilities + regular phone calls to provide updates on their well-being and if they started a treatment). Given the lack of research on the effect of SE on Psychological Safety in this population, while SE has not yet been introduced into the Swedish health care system, special consideration will be given to participant safety, feasibility and acceptability of the SE-treatment. This includes monitoring (and assessing) for serious adverse events (SAEs) and adverse events (AEs), if conducting an RCT on SE in our target sample is feasible (e.g., achieving the target sample goal, assessing attrition rates and session attendance) and the acceptance of the used SE intervention (e.g., positive evaluations and willingness to recommend the treatment). Next to assessing safety, feasibility and acceptability, preliminary outcomes (self-report and experimental measures) will be evaluated at pre-treatment, post-treatment (20 weeks after pre), and at a 20-week follow-up, assessing primary outcomes (Psychological Safety) and secondary outcomes (Social Safeness, PTSD, CPTSD, Depression), as well as additional factors (e.g., interoception) that could contribute to decreased mental health and social functioning issues. Additionally, participants' behavioral (e.g., interpersonal distance) and physiological responses (HR, HRV, EDA) to social stimuli will be assessed pre- and post-treatment in an experimental setup to explore SE's potential to reduce Negative Affect and increase Positive Affect (Activated, Relaxed, Safe/Content) in response to social stress.