Automation is currently a topic of great interest. Part of the reason for this may be that problems associated with operator use of automation can be relatively subtle yet severe. When designing an automated system, it may not be obvious how the interactions between the operator, the system, and the environment may lead to errors. Consequently, those who design and certify flight deck systems should be aware of some of the issues associated with pilot use of automation. These include the potential for over reliance or under reliance on automation and the factors that can contribute to them, issues of pilot and automation authority, automation complexity, feedback, and transitions between automated and manual control. In this paper, we concentrate on how pilots make decisions to use or not use automation and the factors that can influence these decisions.