How does Reddit count unique views of a post? How does Chrome mark a website fraudulent? Will they loop through a huge list of rows and extract the relevant ones? The answer is no: they employ probabilistic data structures to accomplish these tasks that would be impractical with traditional programming methods and algorithms. In this session we will understand what probabilistic data structures are and look at 3 real-world applications which you can start using today. From gigabytes to kilobytes, from minutes to seconds: a journey into ingenious algorithms that changed computing forever.