In May 2014, Presh Talwalkar made a YouTube video about how to multiply numbers by drawing lines. By the end of the month, the video received over a million views. Multiplying by lines is an innovative visual method to multiply numbers. It works like magic and gets people excited about math. This book illustrates how you can multiply by lines, enumerates the precise steps in the process, and offers examples of how to use the method. There are also novel applications of how one diagram can solve additional problems and how multiplying by lines can be used for algebraic expressions. The book includes 35 exercises with solutions.