This document discusses different techniques for merging files in revision control systems. It begins by introducing the concept of merging as reconciling multiple changes made to files. It then discusses external sorting techniques that can handle large amounts of data. The main merging techniques covered are two-way merging, three-way merging, and k-way merging. Two-way merging considers differences between two files alone, while three-way merging also looks at the original parent file. Three-way merging is generally more reliable with less need for user intervention. K-way merging uses a tournament sort algorithm to merge an arbitrary number of files.