OBJECTIVES: To explore staff perceptions of the impact of 'modernization' on the organization, delivery and culture of adult critical care services in England. 'Modernization' policies aimed to alter the boundaries around critical care and create a comprehensive, seamless service. METHODS: Seven hospitals (three teaching and four district general hospitals) in three critical care networks participated. In-depth interviews were conducted with a purposive sample of 45 critical care staff. Data were analysed thematically. RESULTS: The boundaries around critical care were generally perceived to be less fixed than previously. The re-framing of 'internal walls' within hospitals was associated with the introduction of outreach teams, new hospital-wide remits for intensive care unit (ICU) staff and the greater integration of allied health professionals into the critical care team. Transformation of services was challenged by practicalities including the need for additional staff, and a 'them and us' attitude between ICU and ward staff. 'External walls' between hospitals were breached where local clinical networks were perceived to have successfully improved communication and joint working. This was facilitated by effective leadership, availability of network-associated funds, the identification of common problems and evidence of benefit from cooperation. However, barriers existed and there was some scepticism among staff as to whether critical care can ever be entirely 'without walls'. CONCLUSIONS: Policies to remove boundaries around adult critical care are perceived to have had a dramatic impact on the organization of the service. Considerable progress was reported towards developing comprehensive critical care services both within and between hospitals.