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I previously had a PC and kept my iTunes library and all media on an external hard drive (Western Digital Passport). Now I have a MacBook; how do I open my library now?
Hold Option, launch iTunes, select Choose library... and select the /iTunes/ folder on the external.
I saw some other directions but they indicated a different folder for Mac than the ".itl" extension that they pointed out was for Windows users.
The iTunes library.itl file is the iTunes library database inside the iTunes folder. It is the same name on WIndows and Mac.