How to use Jmol to Study and Present Molecular Structures Angel Herraez The purpose of this book is to compile and organize information, both available from public sources and accumulated through experience, about the use of Jmol software, an interactive viewer for three-dimensional molecular models. The main objective is to provide a guide for those who are starting to take advantage of this program, without forgoing it is a handbook for more experienced users to consult and to progress. It is my hope that it might be useful to instructors, authors of teaching materials or popularization of science, students, researchers, and administrators or designers of information portals. The guiding criterion followed while designing this handbook is to avoid a systematic and detailed description, in an encyclopedic format, of each and every possible action and command available in Jmol; such an approach corresponds to the official "reference guides" of the program, accessible in the internet. Due to the rapid evolution that Jmol is experiencing and to the fact that it is being developed by volunteers, the user-friendly documentation does not progress at the same pace, and that which is produced is rather technical, concise and fit for those who are already familiar with the software and with programming languages in general. More so, it is unlikely that a novice user will access information about capabilities whose existence he or she doesn't know of yet, or for which he or she does not know the relevant command. According to this - perception of the situation, as well as to the great diversity of actions possible in Jmol, the book has been organized in sections oriented with the aspiration of being useful for gradual, stepped learning and progress. Therefore, we start with The most easy-to-use commands and those which presumably will be needed more often, and then progressively advance into more rarely used commands, or those applicable only in specific fields, or those that are more difficult to comprehend and use. At the same time, occasionally in these pages I have given up the explanation of all possible ways of doing something, instead simplifying the description to a single one, advisable in my opinion for the sake of simplicity. […]