.NET Excel Library that can read/write .xls files [closed]

I'd recommend NPOI. NPOI is FREE and works exclusively with .XLS files. It has helped me a lot.

Detail: you don't need to have Microsoft Office installed on your machine to work with .XLS files if you use NPOI.

Check these blog posts:

Creating Excel spreadsheets .XLS and .XLSX in C#

NPOI with Excel Table and dynamic Chart

[UPDATE]

NPOI 2.0 added support for XLSX and DOCX.

You can read more about it here:

NPOI 2.0 series of posts scheduled

Is there a reason why you can't use the Excel ODBC connection to read and write to Excel? For example, I've used the following code to read from an Excel file row by row like a database:

private DataTable LoadExcelData(string fileName)
{
  string Connection = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + fileName + ";Extended Properties=\"Excel 12.0;HDR=Yes;IMEX=1\";";

  OleDbConnection con = new OleDbConnection(Connection);

  OleDbCommand command = new OleDbCommand();

  DataTable dt = new DataTable(); OleDbDataAdapter myCommand = new OleDbDataAdapter("select * from [Sheet1$] WHERE LastName <> '' ORDER BY LastName, FirstName", con);

  myCommand.Fill(dt);

  Console.WriteLine(dt.Rows.Count);

  return dt;
}

You can write to the Excel "database" the same way. As you can see, you can select the version number to use so that you can downgrade Excel versions for the machine with Excel 2003. Actually, the same is true for using the Interop. You can use the lower version and it should work with Excel 2003 even though you only have the higher version on your development PC.