Golf is a very popular sport with approximately 289,120 people playing golf in Ireland(European Golf Association, 2008). The amount of scientific research that has been conducted into the biomechanics of the golfer and club is limited, with the majority of the research focusing on the golf drive. The purpose of this study was to identify the biomechanical performance determining factors of the 5-iron golf swing when hitting for maximum distance. Golfer joint kinematics, club swing characteristics and weight transfer data were obtained from thirty male golfers. This data was collected using a twelve camera (250 Hz) motion analysis system (Vicon, Oxford Metrics, UK), Pro V Swing Analyser (Golftek, USA) and a pressure plate (100 Hz) (RSscan Lab Ltd., UK). Participants were divided into two groups, based on their ball launch speed (high vs. low). Those in the high ball speed group were deemed to be the more skillful group. Statistical analysis was used to identify the variables which differed significantly between the two groups, and could therefore be classified as the performance determining factors. Eight key events were identified during the swing for analysis (take away, mid backswing, late backswing, top of backswing, early downswing, mid downswing, ball contact and mid follow through). Significant differences were found between the two groups for club speed, club impact point, the majority of the measured joint angles and angular velocities (X Factor, shoulder, elbow, wrist, hip and knee) and weight transfer at a number of the key events. Two mechanisms are proposed to explain the greater generation of ball speed in the high ball speed group and these are discussed in relation to the results for the individual joint kinematics.