Resumen: The democratisation of online video has opened some exciting opportunities for communicating science in the early 21st century. Businesses, organisations and individuals are all `participants¿ in the new panorama of digital communication, but a distinction is usually made between user-generated content (UGC) and professionally generated content (PGC). This chapter discusses who is really making science videos and for what purpose. Our findings show that online science video producers fit mainly into two categories, depending on the characteristics of the topic. Among topics that are portrayed in the media as current affairs (climate change, vaccines), videos produced by mass media prevail. On the contrary, among those topics that are not news, videos produced by scientific institutions and UGC are more prominent (nanotechnology). Traditional genres and informative contents prevail among videos produced by mass media and scientific institutions, while new genres and entertainment appear mainly in UGC. Scientific institutions have the challenge of capturing the attention of thriving online audiences, being more visible and adapting content to formats that are not exclusively informative.