Fat (i.e., adipose tissue) is one of the most misunderstood, controversial organs in the body. Not a day goes by without it making the headlines or ‘breaking’ the Internet. Reports about the world’s healthcare system being crippled by preventable obesity-related diseases jostle against advocates’ calls for fat acceptance, while the masses witness improbably sculpted bodies strut along the red carpet and photographs of celebrities supposedly falling off the ‘slim’ wagon. Fat means very different things to different people and is routinely conceptualized in everything from biological, medical, epidemiological, social, economic, and aesthetic, to moral terms. This multi-dimensionality makes it inherently fascinating, controversial, and emotive, but the abundance of studies and conflicting narratives have also resulted in great confusion and uncertainty about fat. Waisted provides an opportunity to re-centre our understanding by reviewing the biology of adipose tissue, exploring its important relationship to body shape and metabolic health, and considering the myriad social meanings of this enigmatic organ.