The aim of this study is to characterise the use of clinical nutrition support, especially of parenteral nutrition that is administered directly into a vein, in adult patients with critical illness. The study wants to assess nutritional balance (that means the ratio of calories and protein prescribed to calories and protein actually received). Furthermore, it wants to evaluate whether the nutrition received has influence on the patients' clinical outcome, with focus on measures of physical function, such as capability of conducting daily living activities. As the study is "observational", no specific medications or treatments will be provided as part of the study to the patients.

Study patients will be observed during their stay on an intensive care unit, for a maximum duration of 15 days. Furthermore, questions on the well-being of the patients will be asked via telephone interviews 30 and 90 days after their admission to the intensive care unit.

Data of approximately 1250 patients will be collected and evaluated in this study, from approximately 100 hospitals in 11 European countries (Austria, Belgium, Czech Republic, France, Germany, Hungary, Italy, Poland, Spain, Sweden and United Kingdom).

Inclusion Criteria:

1. Age ≥18 years and ≤95 years, male or female
2. Hospitalised in a medical, surgical, or trauma ICU for at least five consecutive calendar days and either admitted to the ICU during the predefined screening month or admitted to the ICU maximally 4 days before start of the screening month
3. BMI ≥18.5 kg/m2 and ≤45 kg/m2
4. Written informed consent or requirements of local/national ethical committee

Exclusion Criteria:

1. Burn injury
2. Pre-existing neuromuscular or psychiatric disorders that preclude proper assessment of functional status
3. Severe hypoxic brain injury or severe neurological diagnosis (e.g. meningitis, encephalitis, brain trauma, spinal cord injury) at the time of ICU admission that precludes proper assessment of functional status
4. Receiving home parenteral nutrition at the time of ICU admission (e.g. due to short bowel syndrome)
5. Receiving home enteral nutrition (tube feeding) at the time of ICU admission
6. Chronic invasive or chronic non-invasive ventilatory support before ICU admission
7. Patients with a legal representative in place before ICU admission
8. Admission to the ICU for palliative care
9. Previous participation in this study (if the screening month is repeated and a patient is re-admitted to the ICU during the repeated screening month, only ICU data collected for that patient during the original screening month will be included)
10. Concurrent enrolment in a nutrition-related interventional study at the time of screening

The study population will include adult male and female patients with critical illness (i.e. patients requiring pharmacological and/or technical support to treat a vital threat) who are hospitalised in a medical, surgical, or trauma ICU for at least 5 consecutive calendar days.