I am using a workbook with thousands of lines. Some data is very old and
either missing or or out dated. In particular I am looking to find the
ship_date for each project_id. There is another worksheet that has about 80%
overlap with my workbook. How can i get the good ship_date information from
the other workbook into my workbook, and how can I see which project_ids are
missing in my workbook so I can add those rows?

ken

Ken,

This sounds like you want to use the VLOOKUP function.
Workbook A contains thousands of lines with outdated information, and you
wish to pull the correct information from Workbook B. I will assume that
Workbook A and B contain the Project_ID in Column A, and Ship_Date in Column
B.