You can create an .IDX index file by including the TO idx file clause. The index file is given the default extension .IDX, which can be <b>overridden by explicitly including a different extension or by changing the default index extension in the FoxPro configuration file</b>. Standard MS-DOS rules for naming files must be observed when creating index files.All 'INDEX ON acct_no TO t$000000.tdx' is doing is creating an IDX type index called 't$000000.tdx' on field 'acct_no' giving the index file an extension of .TDX instead of .IDX.