This is a prospective, multi-center, observational study of adult patients (≥18 years old) admitted to ICUs. Generally, all patients admitted to the ICU for any indication will be considered at risk for developing HABP/VABP. A subset of the at-risk patients treated with select respiratory modalities for at least 12 hours will be considered high risk for the development of HABP/VABP, will have baseline data collected, and will be screened daily for antibiotic treatment for suspected pneumonia. Patients not meeting high-risk criteria, "other-ICU patients", will be screened twice weekly for antibiotic treatment for suspected pneumonia.