Torin Alter presents a compelling defence of the ‘knowledge argument’ against physicalism, pioneered by Frank Jackson. According to physicalism, consciousness is a physical phenomenon. The knowledge argument stars Mary, who learns all objective, physical information through black-and-white media and yet acquires new information when she first sees colors for herself: information about what it is like to see in color. Based partly on that case, Jackson concludes that not all information is physical. Alter argues that the knowledge argument succeeds in refuting all standard versions of physicalism: versions on which consciousness is grounded by what objective science reveals. Alter also argues that given further, plausible assumptions, the knowledge argument leads to Russellian monism, according to which there are intrinsic properties that both constitute consciousness and underlie properties described by physics, such as mass and charge. Alter explains how the knowledge argument establishes those two conclusions and defend it against numerous objections.