Critical ill patients in the Intensive Care Unit (ICU) require a high amount of care. Due this complex and specific care they can take care for only a limited number of patients per shift. In this thesis we focus on the importance of nursing workload for the planning of nursing staff and the impact of COVID on both the workload and planning of nursing staff. With a systematic review we identified the Nursing Activities Score (NAS) as the best performing system for measuring nursing workload and planning of nursing staff. However, the NAS is somewhat outdated and overestimates the nursing workload. For this reason, we recommend further recalibration of the NAS. Workload is also perceived differently by nurses compared to the objective nursing workload as measured with NAS. Both the severity of illness of the patient and being a student nurse were factors that increase the perceived nursing workload. It is important to find the optimal nursing workload per nurse. A NAS-score around 80 points per nurse leads to a significant higher chance of a nurse being satisfied. A further increase of both the objective and perceived nursing workload to a very high or a low workload diminish these positive associations. Our last study showed the impact of COVID-19 on the nursing workload. Nurses were confronted with both a significant higher number of patients per nurse and a significant higher NAS per nurse in the COVID-period compared to the non-COVID period. Our results should be considered in planning the nursing staff; both a too low and a too high nursing workload should be avoided to keep the job position of an ICU nurse attractive. Further validation of an optimum nursing workload and the development of national guidelines about nursing capacity and workload per nurse is recommended.