Difference between Actions and Functions

Actions are unique to QTP while functions are supported by both VB Script and QTP. Actions can optionally pass and receive input and output parameters. When used, input parameters must be passed first, followed by output parameters. A parameter cannot serve both as an input as well as an output parameter. In addition to supporting output parameters, Action can also return a value. An object/array can't be use as an action parameter. Lastly Actions are maintaining object repository where as functions are not.