**Study Summary** This study looks at *Chronic Lymphocytic Leukemia (CLL)*, a common type of blood cancer in adults. The study focuses on a medicine called **acalabrutinib**, which helps treat CLL. The medicine was approved in Europe in 2020 and has been used in Italy since 2021. This study aims to understand how well the medicine works in real-life situations. The study is observational, meaning doctors watch and record how patients respond to the medicine without changing their usual care. It involves patients who started taking acalabrutinib in Italy between May 2021 and April 2022. Doctors will look at patient records to see how long they take the medicine and why they stop. The study will follow patients for up to 5 years. **Key Points:** - The study lasts up to 5 years, and doctors will collect data from patient records five times. - Only adults diagnosed with CLL and who started acalabrutinib treatment during the specified dates can join. - Participants must give their consent to be part of the study. This study helps doctors understand how acalabrutinib works in everyday settings, which can improve future CLL treatments.