In the Netherlands, long-term community psychiatric treatment for patients with a severe mental illness (SMI) is poorly developed and lacks a structured, goal-centered approach. Often this form of treatment is provided by community mental health nurses (CMHN’s). Especially in the group of nonpsychotic patients with SMI, it often leads to care-as-usual with limited proven interventions and an unstructured treatment. Interpersonal Community Psychiatric Treatment (ICPT) was developed to provide this group of patients a focus, a theoretical view, and a methodological structure. A pilot study has been conducted on ICPT. As a result, a randomized controlled trial (RCT) was recently conducted in which this study is part. The pilot study showed improvement on a number of treatment outcomes. However, the working alliance (WA) experienced by the patients, although not significant, was considered to be decreased. The aim of study was to gain insight into how the ICPT-elements shape the WA and the possible self-determination of patients in general. The main part of this mixed-methods study was a qualitative study with a Grounded Theory approach. For the selection of the participants, quantitative data from the current RCT has been used. Semistructured interviews have been conducted with 13 participants, divided over three mental health institutions throughout the Netherlands. Interviews and analysis were alternated, so that the interview topics were developed by constant comparison. Eleven participants were female and 11 participants received social benefit. Six of the participants were above 50 years of age. Four participants suffered either from a depressive or anxiety disorder. Seven participants had a borderline personality disorder. The results are linked to Bordin’s theory of the therapeutic alliance, which is agreement on therapeutic tasks, agreement on therapeutic goals, and the quality of the personal bond. The WA could be analyzed from three different perspectives: mutually agreed on goals, tasks, and experienced interpersonal relationship. ICPT had limited influence on the mutually agreed on goals and interpersonal relationship but mainly on the mutually agreed on tasks. In daily practice, ICPT may have a positive influence on the perceived WA. The main factors that affected the perceived WA during ICPT were the tasks that had been mutually agreed on, the use of an agenda, the structure of the sessions, the alliance between the CMHN and the patient, and the patient’s own self-determination. There was a limited influence on the mutually agreed on goals and the quality of the personal relationship between the CMHN and the patient. The present research revealed valuable information about the significance of the WA in ICPT and the opinions of the respondents about ICPT and information about what might be helpful or unhelpful in their relationship with their CMHN.