This is a complimentary chapter from the textbook, ICU Liberation, Second Edition ), titled "Introduction to the Bundle." The Society of Critical Care Medicine (SCCM) has endorsed and published the 2013 Pain, Agitation, and Delirium (PAD) guidelines and the 2018 Pain, Agitation, Sedation, Delirium, Immobility, and Sleep Disruption (PADIS) guidelines, which outline the best evidence available for addressing pain, agitation, delirium, early mobility, and sleep. Many ICUs have found adoption of the PAD and PADIS guidelines difficult in practice, either as individual components or when integrated with other aspects of patient care. Because of the difficulties found with implementation of the guidelines, an evidence-based, bundled approach was developed to aid in the clinical application of the PAD and PADIS guidelines, called the ICU Liberation Bundle. This bundle was formerly referred to as ABCDEF, a mnemonic representing the key bundle elements: A for Assessment, prevention, and management of pain; B for Both spontaneous awakening trials and spontaneous breathing trials; C for Choice of sedation and analgesia; D for Delirium assessment, prevention, and management; E for Early mobility and exercise; and F for Family engagement and empowerment. The ICU Liberation Bundle has been studied in more than 20,000 patients, demonstrating a reduction in ICU days, hospital days, next-day mechanical ventilation, coma, delirium, hospital mortality, use of physical restraints, ICU readmissions, transfer to a facility, and healthcare costs. Despite several studies demonstrating the benefit of compliance with the ICU Liberation Bundle, global implementation within the ICU has not yet been established.