Jmol is an interactive viewer for molecular models in the computer. This book aims to be both a tutorial for beginners and a handbook for reference and deepening for more skilled users. It may be of profit for instructors, content authors, students, researchers, and administrators or designers of information portals. The book is organized in sections for a gradual learning curve. It starts with the simplest and most frequent commands and then advances into the occasional, specific and more complex ones. There are sections addressed to those who only need occasional and basic use, another that explains how to take advantage of the command language -split into two levels and further continued on vol. 2- and, finally, a section only needed by those interested on preparing web pages to present models to others. A command index is included, as well as a glossary and a listing of reference addresses in internet, including that of the companion website created for this book.