You have to put your hash out of the while loop.

#!/usr/bin/perl -w
use strict;
use Data::Dumper;


my %IACISBN_ENUM;

while ( my $line = <DATA> ) {
    chomp($line);

    my ( $IacIsbn, $Title, $EPI, $BundleCode ) = split( "\t", $line );

    $IACISBN_ENUM{$IacIsbn} =
      { 'Title' => $Title, 'EPI' => $EPI, 'Bundle' => $BundleCode };

}
print Dumper \%IACISBN_ENUM;

__END__
IacIsbn Title   EPI     BundleCode
[download]

hth,
PooLpi