IDL does not have a library for reading and writing SEG-Y files. The 'IDLffSEGY' library, I notice, is one of the freeware libraries that has been uploaded to ITT Visual Information Solutions' 'Code Contribution Library' site. I notice from that library's "home page", however, that it only "...provides read support for the SEG-Y file format." That is, it is not a library that provides a SEG-Y writer. If all you need to do is to share your 'IDLffSEGY' object from one IDL session with a future IDL session (or with some other user), then you should do this with IDL's SAVE procedure. Make sure, however, to read the second note in the Online Help for the 'SAVE procedure reference' about saving object instance variables. If, on the other hand, you need to write out data created in IDL as a SEG-Y format file, then the library download from our Code Contribution Library site will not help out. James Jones