The 21st Century FTC Act would expand the Federal Trade Commission's authority to regulate unfair and deceptive business practices. The bill gives the FTC broader power to write rules about what constitutes unfair or deceptive conduct through a standard notice-and-comment rulemaking process, similar to how other federal agencies create regulations. It also strengthens the FTC's ability to impose civil penalties on companies that violate these rules or the FTC Act itself. The legislation simplifies certain procedural requirements the FTC currently must follow when creating these rules and clarifies the legal standards courts should use when reviewing whether the FTC's actions are supported by evidence. This bill primarily affects businesses engaged in commerce, as it increases regulatory oversight of their marketing and sales practices, while giving consumers potentially stronger protections against deceptive conduct.