This thesis presents research to document the physical activity, training and match demands, nutritional intake, and dietary habits in female adolescent hockey players. In Study 1, 24 female adolescent hockey player’s body mass and stature were measured and developmental age calculated and compared with measures of physical performance. Participants were average developing but 90% were still growing. Physical performance measures were above population means, in line with other studies in young athletes but below elite adult female hockey players. From all measures it was concluded that adolescent female hockey players at the bottom of the England hockey selection pyramid would fit the IOC definition of an adolescent athlete. Study 2 used GPS and heart rate monitors to quantify physical demands of 45 players in U16 League Games. Distance covered and pitch time were comparable to International U16/U17 and sub-elite adult games, but the intensity of play was lower. From this study coaches working with adolescent female hockey players would be advised focus on the intensity of play in preparation for higher and adult leagues. In Study 3, 24 female adolescent hockey players completed a 4-day self-report food and physical activity diary. Total energy, carbohydrate, fruit and vegetable portions and fibre were all lower than guidelines, and saturated fat and sugar intake were higher than recommended. Protein intake was adequate but poorly distributed across the day. On the back of this data, in line with the National Diet and Nutrition Surveys (2012-2020), practitioners working with this age group should initially focus on population healthy eating advice, increasing fruit and vegetable intake and ensuring adequate protein availability across the day. Study 4 used an online questionnaire to document habitual eating behaviour and physical activity levels in 162 female adolescent hockey players. Participants played 21 different sports. Physical activity was classified as moderate overall and high in the evenings and weekends. Most participants ate breakfast and a cooked lunch, but there was evidence that eating behaviour was impacted by sports participation and this should be taken into account when planning sports training schedules and nutrition education. Study 5 concurrently measured physical activity (accelerometer and GPS), nutritional intake (food diary), nutrition knowledge and eating behaviour (surveys) in 29 female adolescent hockey players over seven days. The regular sports training and competition contributed to players high energy expenditure, which was not matched by energy intake. Dietary quality was poor with high intake of saturated fat and added sugar and low fibre intake. In summary, the research in this thesis presents novel data on anthropometric and physiological characteristics, training and match loads, physical activity, nutritional intake, and dietary habits of female adolescent hockey players which can be used to inform evidence-based guidance for players, parents, schools, and coaches.