Most professionals and lay people would probably argue that they know what child pornography is. While it is a relatively easy concept to define when one refers to the “typical” forms (e.g. a photograph of a pre-pubescent child engaged in a sexual act), it becomes less easy to define when the image is less graphic (e.g. a photograph of a 16-year-old girl topless). This article considers the challenges that arise when drafting an adequate legal instrument to tackle child pornography. It considers at what age a person is “a child”, what types of material should be considered as pornography and what it is about material that makes it child pornography. The article concludes that child pornography is not an easy concept to define and that tension will always arise between the desire to criminalise exploitative material and personal freedoms such as expression and free speech.