For MEGA to read and interpret your data correctly, it should be formatted according to a set of rules. All input data files are basic ASCII-text files, which may contain DNA sequence, protein sequence, evolutionary distance, or phylogenetic tree data. Most word processing packages (e.g., Microsoft Word, WordPerfect, Notepad, and WordPad) allow you to edit and save ASCII text files, which are usually marked with a .txt extension. After creating the file, you should change this extension to .meg, so that you can distinguish between your data files and the other text files. Because the organizational details vary for different types of data, we discuss the data formats for molecular sequences, distances, and phylogenetic trees separately. However, there are a number of features that are common to all MEGA data files.