In a world mediated through computing, our everyday lives are increasingly affected by complex and invisible systems. Some of these are algorithmic trades on the stock market, others are search results for information, movies, or a date. These systems often aspire to transparency, usability, and efficiency. Playful systems take a different approach, bringing the systems to the foreground as games, stories, narratives, and visualizations. Playful systems embrace complexity rather than conceal it, and seek to delight, not disappear.