Contemporary art can seem chaotic: it may be made of toilet paper, or candies you can eat, or meat that is thrown out after each exhibition. Some works fill a room with obsessively fabricated objects, while others purport to include only concepts, thoughts or language. I argue, through many examples, that disparate developments in installation art, conceptual art, time-based media art, and participatory art can be understood in terms of custom rules. Many artists articulate custom rules governing artwork display, preservation of material elements, and interactivity or audience participation. Rules are established through the artist’s sanction: the creative act of designating the material elements and rules that constitute the work’s structure. Rules serve as medium: they are part of the work’s structure and help to constitute its meanings. Rules are meaningful in themselves, and they help to activate the expressive potential of material objects. Museum practice should include providing information about the rules; otherwise, audiences can’t fully appreciate the work. Contemporary art conservation involves preserving information: loss of information about the rules, like loss of a chunk of marble, can seriously damage the work. Rules are trickier to pin down than material objects and are subject to violation, so we’ll examine the effects on the work’s integrity and authenticity when things go wrong in various ways. Is the emergence of custom rules a positive development? Some artists have used rules to powerful effect. But rules aren’t always used well: bad art can take any form.