EES ('ease') is a revolutionary program which will change the way you think and work. EES provides capabilities not found in any other equation solving program. EES will solve large sets of non-linear algebraic and differential equations. EES also provides publication-quality plots, linear and non-linear regression, optimization, unit conversion and consistency checking, and uncertainty analyses. Built-in functions are provided for thermodynamic and transport properties of many substances, including steam, air, refrigerants, cryogenic fluids, JANAF table gases, hydrocarbons and psychrometrics. Additional property data can be added. EES also allows user-written functions, procedures, modules, and tabular data. EES can also interface with REFPROP and other NIST fluid property programs. REFPROP provides the most advanced methods for estimating the properties of mixtures. The Professional version allows many other additional features including animation and the ability to make stand-alone programs.