This chapter examines errors and antecedent’s characteristic of multi-operator teams operating complex systems. Complex systems often require multi-operator teams, two or more operators working towards a common goal or objective. Using multiple operators also gives operators the flexibility to share system control duties as needed, which helps balance individual workload as operating cycles change. The operator with the inaccurate situation assessment could then create a multi-operator team error by interfering with the assessments of other team members. Many complex systems assign more than one operator to control the equipment. Physiological and behavioural antecedents that lead to errors in single-operator systems can affect multi-operator teams as well. The quality of a company's procedures can also affect the quality of team member interaction and serve as an antecedent to multi-operator team errors.