In the UK, women are increasingly underrepresented in academic STEM careers. Of all Professors in STEM in the UK, only 22% are women. This thesis conducted an exploratory investigation into the individual and organisational factors that contribute to women's successful career progression in academic STEM careers. Semi-structured interviews with 71 UK based women who had all been promoted to Professor or more senior roles in STEM led to the identification of five master themes: 1 - Gendered experiences in academic career progression; 2 - The promotional process to professor; 3 - Role models are good, mentors are better, but sponsors are best; 4 - Workload Overload, 5 - Work-Life Balance. This also led to a proposed model of layered barriers to career progression. Structural, organisational factors were identified as having far more impact on inequality in retention and career progression of women in STEM than their individual characteristics.