This thesise xaminess omeo f the measurementc, onceptual,p redictive, and intervention issues surrounding transformational leadership theory. Chapter 1 reviews the researchli terature on transformationall eadershipa s it relatest o the above issues. This review identifies several questions worthy of future investigation: (1) How should transformationall eadershipb e conceptualiseda nd measured?(2 ) What exactly do transformational leaders provide their followers with? (3) To what extent are the different transformational leader behaviours modifiable? and (4) Do transformational leadership interventions result in high levels of follower and organizational outcomes? Chapter 2 contains two studies that explore a differentiated conceptualisation of transformational leadership, the predictive qualities of the different transformational behaviours, and the extent to which the different transformational leader behaviours are malleable. A total of 636 participants (Royal Marine Commando recruits undergoing basic training) took part in these studies. Specifically, Study 1 used a correlational design to identify an appropriate measurement model and what the important transformational leader behaviours were, i. e., the behaviours that were significant predictors of successful completion of training (contingent reward, fosters acceptance of group goals, appropriate role modelling, inspirational motivation, and individual consideration). This information (as well as the level of use of the different behaviours) was then used to inform the intervention in Study 2. Study 2 used a mixed model design to assess the efficacy of a differentiated transformational leadership intervention. The results revealed that, in comparison to the control group, the intervention group's followers rated their leader as being higher in three of the four behaviours that were identified in Study 1 as being important (fosters acceptance of group goals, individual consideration, and contingent reward). The recruit self-report variables of self-confidence, resilience, and satisfaction were also higher in the experimental group compared to the control group. Unfortunately, for various reasons objective performance data was not available. Chapter 3 describes a large scale longitudinal experimental study that included objective performance/outcome data. A total of 3468 participants (Infantry recruits undergoing basic training) took part in this study. Chapter 3 was an organisation wide study where approximately half the organisation formed the intervention group and the other half formed the control group. Study 1 identified the important leader behaviours in Infantry recruit training (contingent reward, inspirational motivation, fostering acceptance of group goals, and individual consideration). Study 2 then sought to increase the important behaviours that were identified in Study 1. The results of the intervention study revealed that six of the seven leadership behaviours examined were positively affected by the intervention (high performance expectations was not targeted or impacted by the intervention). Follower outcomes (self-confidence, resilience, satisfaction, and group cohesion) and organizational outcomes (1s` time pass rates, total pass rates, and remedial pass rates) were also positively affected by the intervention. Chapter 4 contained three studies that examined the proposition that transformational leaders provide their followers with vision, support, and challenge. A total of 1212 participants (Infantry recruits undergoing basic training) took part in this study. Studies 1 and 2 explored the theoretical rationale and internal validity of the proposed model. Study 3 then tested the predictive validity of the vision, support, and challenge model. The results revealed that vision, support, and challenge demonstrated acceptablele vels of internal consistencya nd differentially predictedt he outcomes included in the study (leader inspires extra effort, satisfaction, self-confidence, and performance). The final chapterd iscussesth e findings of the thesisa nd provides suggestionsf or future research.