Gender imbalance in computing education is a well-known issue around the world. For example, in the UK and Ireland, less than 20% of the student population in computer science, ICT and related disciplines are women. Similar figures are seen in the labour force in the field across the EU. The term "leaky pipeline" is often used to describe the lack of retention of women before they progress to senior roles. Numerous initiatives have targeted the problem of the leaky pipeline in recent decades.This paper provides a comprehensive review of initiatives related to techniques used to boost recruitment and improve retention among women in undergraduate computer science and computing courses in higher educational institutions. The review covers 350 publications from both academic sources and grey literature sources including governmental guidance, white papers and non-academic reports. It also includes sources in languages other than English.The primary aim was to identify interventions or initiatives (which we have called "actions") that have shown some effectiveness. A secondary objective was to structure our findings as a categorisation, in order to enable future action discussion, comparison and planning.A particular challenge faced in a significant portion of the work reviewed was the lack of evaluation: i.e. the assessment of the direct relationship between the initiatives undertaken and the outcomes on retention or recruitment. There are only a limited number of studies that include a control group and these tend to focus on one particular intervention or action. In addition often the work presents a number of actions that were implemented and it is difficult to determine which action produced most impact. Considering these challenges, actions were identified that had some level of evaluation with positive impact, including where the evaluation was by measuring feedback.The actions were categorised into four groups: Policy, Pedagogy, Influence & Support and Promotion & Engagement. Policy actions require support and potentially structural change and resources at organisation level. This can be at a department or school level within a higher level institution, and not necessarily just at the higher institution level. Pedagogy related actions are initiatives that are related to the teaching of computer science and technology in terms of curriculum, module delivery and assessment practice. The Influence and Support category includes actions associated with ways to influence women to choose computing at third level and once enrolled to support and encourage them to stay in the field. Finally, Promotion and Engagement actions are initiatives to promote computer science and technology based courses and involve engagement and outreach with external stakeholders such as industry, communities and schools.We present our categorisation, identifying the literature related to actions under each category and subcategory. We discuss the challenges with evaluating the direct impact of actions and outline how this work leads toward...