The drivers of employee engagement

Engagement is a frequently used and fashionable term. Some companies now have 'engagement models' and are attempting to measure levels of engagement, perhaps to input to the balanced scorecard, or for incorporation into the human capital report. Research into engagement, however, is almost non-existent. It appears that 'engagement' is not a recognised academic construct, yet all of us feel intuitively that we understand what it means. If engagement can be defined and measured, what drives it? What persuades the employee to 'go that extra mile' - and what does the organisation need to give in return?