Questions on changing Mathematica expressions of one type or format to another, for example date formats, Boxes and other typesetting representations, or different units of measurements.
Although everything in Mathematica is an expression, different kinds of expression have their own internal format or logic, and there are times where one might want to convert an expression to another representational form. The most common case would be to change the way a particular expression is displayed.
Typesetting representations
Mathematica allows for two-dimensional mathematical typesetting and other highly formatted output. It is possible to convert between String, normal StandardForm output and typeset Box representations using the ToString, ToExpression and ToBoxes functions.
Date/Time representations
Mathematica can represent dates in both seconds-since-1900 format and DateList format ({year, month, day} or {year, month, day, hours, minutes, seconds}. All the elements should be integers, except the seconds. As noted in the answer to this question, these formats can be easily converted between each other using the DateList and AbsoluteTime functions.
