The introduction of modern technology in almost every human environment imposes higher cognitive demands on people pegorming everyday tasks. This is why mental workload is a topic of increasing importance. There is no agreement on the definition of mental workload, nor any unit of measurement. It is usually assessed through un array of methods that focus on items ranging from its possible sources to the opinions of the people performing a specific task. Mental fatigue (induced by infraload as well as by overload) and the mistakes that may arise from it are two of the main consequences that should be analysed fiom the perspective of their ca~ise- that is, information processing. Finally, the paper describes the current attempts to standardize the coiacept of mental workload.