This review aims to examine the core components and main definitions attributed to Comprehensive Sexuality Education, and how these components and definitions can impact implementation within different contexts and at different levels. In the presentation of the review, four cross-cutting issues will be addressed: 1) Broad, but lacking definition. Throughout the literature, CSE is described as being broad, covering a range of topics with the aim of ensuring young people are informed and can make their own decisions. However, in its bid to be holistic, the abstract nature of CSE, means that CSE can be perceived as being broad but without any specific direction or ideology. 2) Comprehensive does not equal inclusive. Although it is regularly cited across literature that CSE should be an inclusive and representative approach, there are many identities and experiences of young people which are neglected within documents and briefs – particularly LGBT+ youth, those who do not fall along culturally dominant heterosexual lines and young people living in conflict. Where CSE does not address the experiences and needs of all young people within a context, it cannot purport to be fully ‘comprehensive’. 3) Can work against itself. Despite there being no clear definition of CSE and the opportunity for somewhat flexible content of programmes and policies as a result of this, the notion of 'Comprehensive Sexuality Education’ is often opposed in many contexts on socio-cultural or religious grounds. CSE advocates tend to emphasise the need to develop CSE with socio-cultural sensitivities in mind but doing so can mean that the degree to which programmes or policies can be deemed comprehensive may be compromised. 4) Guidance remains top-down – for now. At present, much guidance on CSE as an approach comes from multi-lateral agencies and international organisations, which contributes to the concept’s abstract nature. While guidance is still predominantly ‘top-down’, the growing number of programme reports, reviews and shared learning resulting from CSE programmes can support a circular system of guidance, which includes feedback from local and national levels.