I want to reference this cell in another worksheet for my current worksheet, which is calculated by
=[2015_RunRate.xlsx]January!$C$66
However, I wan
You can use Indirect function. E.g.:
INDIRECT("[Book2.xlsx]"&B1&"!$A$1")
Where B1 is a cell containing text string with name of a sheet in the other workbook. Like "January", "February", etc.