Microsoft Excel® forms part of the package Microsoft Of’ce. It is a spreadsheet application that features calculation, graphing tools, tables, and a macro programming language, Visual Basic. The main advantage of Excel is that it has spread and is widely used in industry and academia. Thus, it is a perfect tool or interface not only to perform calculations but also to connect different software so that the end user can interact with Excel, and behind the scenes other software such as CHEMCAD®, MATLAB®, Mathcad®, or GAMS® is running and reporting the results back to Excel. Therefore, we consider that this book should start by presenting the main features of this software and its application to chemical engineering.